Resin composition for thermally conductive material and thermally conductive material

ABSTRACT

The present invention is characterized by a resin composition for a thermal conductive material including a polymer (I), a liquid-state plasticizer (II) and a thermal conductive filler (III) having a thermal conductivity of 20 W/m·K or more, wherein the liquid-state plasticizer (II) is in a liquid state at 25° C., and has a mass loss rate of 2 mass % or less when kept at 130° C. for 24 hours. By using this resin composition for a thermal conductive material, it becomes possible to obtain a thermal conductive material having superior thermal conductivity and flexibility.

FIELD OF THE INVENTION

The present invention relates to a resin composition used for obtaininga thermal conductive material, such as a thermal conductive sheet to beapplied so as to radiate heat, and more particularly, concerns a resincomposition for a thermal conductive material, which is superior inthermal conductivity, flexibility and moldability.

BACKGROUND OF THE INVENTION

A material (thermal conductive sheet), obtained by curing a resincomposition prepared by blending a thermal conductive filler forimproving thermal conductivity, such as alumina and silica, into aflexible resin so as to form a sheet shape, has been used for anapplication for radiating heats generated in the electric/electronicpart and the like by interposing between a heat-generating body, such asan electric/ electronic part, installed in various electric productssuch as personal computers and plasma displays, and a heat-radiatingbody, such as a heat sink, a heat-radiating fin and a metalheat-radiating plate. Generally, in most cases, the surfaces of theheat-generating body and the heat-radiating body are not smooth so that,in order to increase the contact area with them to enhance the thermalconductive efficiency from the heat-generating body to theheat-radiating body, the thermal conductive sheet is required to haveflexibility.

Conventionally, silicone rubber and silicone gel have been used asresins having flexibility; however, problems have arisen in which theseresins are expensive, the curing process requires a long period of timeto cause deterioration in productivity and siloxane having a lowmolecular weight is generated to cause a contact failure in theelectronic parts.

In order to solve the above-mentioned problems, a heat-radiating(thermal conductive) sheet, which is formed by curing a bindercontaining a copolymer having a glass transition point of −30° C. orless and a monomer having an unsaturated bond, has been proposed (forexample, Japanese Patent Application Laid-Open No. 2001-335602).Moreover, aside from this, a non-silicon-based resin composition for aheat-radiating material, which contains a polymerizable monomer mainlycomposed of an acrylic acid ester monomer having an alkyl group withcarbon atoms in a range from 2 to 18, a photopolymerization initiatorand a thermal conductive filler, has been proposed (for example,Japanese Patent Application Laid-Open No. 2002-155110). In theseinventions, however, although the problem of the contact failure inelectronic parts due to generation of siloxane having a low molecularweight is solved, since neither silicone rubber nor silicone gel isused, it is found that the moldability at the time of molding thethermal conductive sheet and the flexibility of the resulting sheet needto be improved, as a result of examinations conducted by the inventors,etc. of the present invention.

Moreover, a thermal conductive sheet, which contains a high-moleculargel such as acrylic gel, a thermal softener that is in a solid state orin a paste state at normal temperature and becomes liquid when heatedand a thermal conductive filler (filler agent) has been proposed (forexample, Japanese Patent Application Laid-Open No. 2002-234952).However, even this thermal conductive sheet has some room forimprovements in flexibility.

Furthermore, an acrylic urethane resin has been known in which anacrylic oligomer having two hydroxyl groups in one molecule and apolyfunctional isocyanate having at least two isocyanate groups in onemolecule are used as the resin composition (for example, Japanese PatentApplication Laid-Open No. 2002-30212).

In the case when these resins are used for manufacturing thermalconductive sheets, the following problems tend to be raised: theresulting composition has high viscosity to cause deterioration inoperability; since it is not possible to blend a thermal conductivefiler at a high blending rate, the thermal conductive property of theresulting thermal conductive sheet becomes low; it takes long todisperse the thermal conductive filler uniformly in a resin by kneading,resulting in deterioration in productivity; and since upon manufacturinga composition, the composition is poor in defoaming property foreliminating air mixed therein, bubbles tend to generate in the resultingheat-radiating sheet to cause deterioration in the moldability andthermal conductive performance.

Moreover, for example, a resin composition which has a urethane bond andis used for coating, and which contains a metal organic compound servingas a urethane reactive catalyst and an acidic substance, has been known(for example, Japanese Patent Application Laid-Open No. 2001-240797).However, this document has no description concerning a thermalconductive material, and with respect to the addition of an acidicsubstance, only its effects as a technique for prolonging the usabletime of a coating composition to be cured by using a urethanecrosslinking reaction are described therein. Moreover, this documentalso has no description with respect to a hardness reduction that occurswhen the composition is exposed to high temperatures for a long periodof time.

Here, (meth)acrylic resins have been widely used as a base resin for athermal conductive material (Japanese Patent Application Laid-Open No.2003-49144, the above-mentioned Japanese Patent Application Laid-OpenNo. 2002-155110, Japanese Patent Application Laid-Open No. 11-269438,etc.); however, in most cases, these (meth)acrylic resins are preparedin the form of a liquid-state resin composition (referred to as acrylicsyrup) in which a (meth)acrylic polymer and a monomer are mixed (forexample, Japanese Patent Application Laid-Open No. 9-67495, etc.), andthe user further subjects this liquid-state resin composition to athermal polymerization (radical polymerization) process or acrosslinking (curing) process with a crosslinking agent to form anet-work structure so that a final (meth)acrylic resin product (a moldedproduct, a sheet, etc.) is formed. Here, a method has also been known inwhich a (meth)acrylic resin is manufactured by using a special catalyst(Japanese Patent Application Laid-Open No. 2000-128911, etc.)

With respect to acrylic syrups of this type, those syrups have beenknown in which, for example, a (meth)acrylic monomer is polymerized intoluene, and after toluene has been removed, a (meth)acrylic monomer isadded thereto to form a liquid-state resin (syrup) and the syrup ispolymerized by using a polymerization initiator (see Examples 7 to 9 inthe above-mentioned Japanese Patent Application Laid-Open No. 9-67495).Moreover, the above-mentioned Japanese Patent Application Laid-Open No.2003-49144 has disclosed a method in which a (meth)acrylic monomer isradical-polymerized in ethyl acetate, and after the resulting matter hasbeen applied on a PET film, the PET film is dried. However, the(meth)acrylic resins, obtained by these methods, contain a solvent(toluene, ethyl acetate, etc.). In other words, although these methodsremove the solvent in the middle of the processes, it is impossible toremove the solvent completely. When the (meth)acrylic resin thusobtained is used, there is a possibility that the residual solvent mightevaporate even little by little, and the possibility becomes greater inthe case of applications (thermal conductive materials and the like) inwhich heat is imposed.

The objective of the present invention is to solve the above-mentionedconventional problems, and consequently to provide a resin compositionfor a thermal conductive material that is superior in moldability, andthe thermal conductive material that exerts a superior thermalconductivity and flexibility for a long period of time.

DISCLOSURE OF THE INVENTION

The present invention relates to a resin composition for a thermalconductive material, which contains a polymer (I), a liquid-stateplasticizer (II) and a thermal conductive filler (III) having a thermalconductivity of 20 W/m·K or more, and the liquid-state plasticizer (II)is in a liquid state at 25° C., and has a mass loss rate of 2 mass % orless, when kept at 130° C. for 24 hours therein.

BEST MODE FOR CARRYING OUT THE INVENTION

A resin composition for a thermal conductive material of the presentinvention (hereinafter, referred to simply as “resin composition”)contains a polymer (I), a liquid-state plasticizer (II) and a thermalconductive filler (III) having a thermal conductivity of 20 W/m·K ormore. By curing this resin composition, a flexible cured product inwhich the liquid-state plasticizer (II) is held among crosslinkingnetwork of the polymer (I) is obtained, and this cured product is athermal conductive material. In the present specification, compoundgroups denoted by different codes indicate different compound groupsunless otherwise indicated.

First, the following description will explain the liquid-stateplasticizer (II) that is an essential component of the resin compositionof the present invention. This liquid-state plasticizer (II), which isin a liquid state at 25° C. and is not mixed with water, is a compoundcapable of plasticizing the polymer (I). With respect to theabove-mentioned liquid-state plasticizer (II), those having a highheat-resistant property are preferably used so as to allow the resultingcured product of the resin composition to exert its flexibility stablyfor a long period of time. With respect to the scale for theheat-resistant property, the present invention uses the mass loss rate(%) [=100×(mass prior to the holding process−mass after the holdingprocess)/mass prior to the holding process] obtained after theliquid-state plasticizer (II) has been held at 130° C. for 24 hours.Here, the present invention uses the liquid-state plasticizer (II) inwhich this mass loss rate is set to 2 mass % or less. The mass loss rateis preferably set to 1 mass % or less, more preferably to 0.5 mass % orless, most preferably to 0.1 mass % or less. With respect to the massloss rate, for example, a liquid-state plasticizer of about severalgrams is put into a container made of a fire-proof material such asaluminum, and kept under an atmosphere of 130° C. for 24 hours, andmasses before and after the storing are measured to determine the rate.

With respect to liquid-state plasticizer (II), low viscosity is includedin its preferable requirements. For example, the viscosity at 25° C. ispreferably set to 1000 mPa·s or less, more preferably to 800 mPa·s orless, most preferably to 500 mPa·s or less, by far the most preferablyto 300 mPa·s, and those having a viscosity value in this level arepreferably used. Here, the viscosity of liquid-state plasticizer (II) ismeasured by using, for example, a B-type viscometer made by Tokyo KeikiCo., Ltd.. The following Table 1 shows a relationship between acombination of rotor Nos. and numbers of revolutions and an upper limitvalue of the measurable viscosity for this B-type viscometer, and as theactually measured viscosity becomes closer to the upper limit value, themeasurement error can be reduced. In the case when the approximateviscosity of a subject to be measured has been known, the combinationbetween rotor No. to be used and the number of revolutions is determinedby reference to this Table 1. In contrast, in the case when theapproximate viscosity is unclear, rotor No. is changed from the biggervalue to the smaller value, with the number of revolutions being changedfrom the low speed side to the high speed side, while the relationshipin the following Table 1 is taken into consideration, so thatmeasurements are carried out in an appropriate range. TABLE 1 Number ofNumber of Number of Number of revolutions revolutions revolutionsrevolutions 60 rpm 30 rpm 12 rpm 6 rpm Rotor No. 1 100 mPa · s  200 mPa· s  500 mPa · s 1000 mPa · s Rotor No. 2 500 mPa · s 1000 mPa · s  2500mPa · s 5000 mPa · s Rotor No. 3 2000 mPa · s  4000 mPa · s 10000 mPa ·s 20000 mPa · s  Rotor No. 4 10000 mPa · s  20000 mPa · s  50000 mPa · s100000 mPa · s 

With respect to liquid-state plasticizer (II), specific examples thereofinclude: a phthalic acid ester-based plasticizer, a pyromellitic acidester-based plasticizer, a trimellitic acid ester-based plasticizer, anadipic acid ester-based plasticizer, a polyester-based plasticizer, anepoxy-based plasticizer, a phosphoric acid ester-based plasticizer and arubber-use plasticizer. Two or more kinds of these may be used incombination.

In most cases, plasticizers, which are superior in heat resistance andsatisfy the above-mentioned requirements for the mass loss rate, areselected from liquid-state plasticizers having an aromatic ring (inparticular, a benzene ring), and examples thereof include: phthalic acidesters, that is, phthalic acid di-C₈₋₁₅ alkyl esters (preferably,phthalic acid d-C₉₋₁₃ alkyl esters) such as didecyl phthalate, diundecylphthalate, and didodecyl phthalate. With respect to trimellitic acidesters, examples thereof include trimellitic acid tri-C₇₋₁₄ alkyl esters(preferably, trimellitic acid tri-C₈₋₁₂ alkyl esters), such as octyltrimellitate, trinonyl trimellitate, and tridecyl trimellitate. Withrespect to pyromellitic acid esters, examples thereof, in many cases,correspond to pyromellitic acid tetra-C₆₋₁₃ alkyl esters (preferably,pyromellitic acid tetra-C₇₋₁₀ alkyl esters), such as tetraoctylpyromellitate, and with respect to phosphoric acid esters, examplesthereof correspond to triphenyl phosphates in which a benzene ring maybe substituted by a C₁₋₃ alkyl group, such as cresyldiphenyl phosphate,tricresyl phosphate and trixylenyl phosphate.

With respect to the above-mentioned liquid-state plasticizer (II),commercially available products may be used, and examples thereofinclude: dinormal decyl phthalate [Vinycizer 105, made by KaoCorporation, etc.], di-C₁₀₋₁₂ alkyl phthalate [Vinycizer 124, made byKao Corporation, etc.], trimellitic acid tri-2-ethylhexyl trimellitate[Trimex T-08, made by Kao Corporation, etc.], trioctyl trimellitate[ADK-Cizer C-8, made by Asahi Denka Co., Ltd., etc], trinormaloctyltrimellitate [Trimex N-08 and Trimex New-NSK, made by Kao Corporation,and ADK-Cizer C-880, made by Asahi Denka Co., Ltd., etc.], triisononyltrimellitate [ADK-Cizer C-9N, made by Asahi Denka Co., Ltd., etc],trimellitic acid triisodecyl trimellitate [Trimex T10, made by KaoCorporation; ADK-Cizer C-10, made by Asahi Denka Co., Ltd., etc.],trimellitic acid mixed alcohol ester [ADK-Cizer C-79, ADK-Cizer C-810,made by Asahi Denka Co., Ltd., etc], tetraocryl pyromellitate [ADK-CizerUL-80, made by Asahi Denka Co., Ltd., etc], pyromellitic acid mixedalcohol ester [ADK-Cizer UL-100, made by Asahi Denka Co., Ltd., etc],cresyldiphenyl phosphate [Kronitex CDP, made by Ajinomoto-Fine-TechnoCo., Inc. etc.], tricresyl phosphate [Kronitex TCP, made byAjinomoto-Fine-Techno Co., Inc. etc.], and trixylenyl phosphate[Kronitex TXP, made by Ajinomoto-Fine-Techno Co., Inc. etc.]. Each ofthese liquid-state plasticizers (II) may be used alone, or two or morekinds of these may be used in combination.

The following description will explain the polymer (I) contained in theresin composition of the present invention. The polymer (I) includes a(meth)acrylic polymer (I-a) and a crosslinking polymer (I-b). When the(meth)acrylic polymer (I-a) is used as the polymer (I), the resincomposition preferably contains a polymerizable monomer (IV).

The (meth)acrylic polymer (I-a) refers to a polymer in which 50% by massor more (preferably, 70% by mass or more, most preferably, 80% by massor more) of constituent units is composed of (meth)acrylic acid esters.Moreover, the “methacrylic polymer” refers to a polymer in which theportion exceeding 50% by mass of the above-mentioned (meth)acrylic acidesters is composed of methacrylic acid esters. The “acrylic polymer”refers to a polymer in which the portion exceeding 50% by mass of theabove-mentioned (meth)acrylic acid esters is composed of acrylic acidesters. Moreover, the polymer contains binary or more copolymers.

With respect to the monomer to be used for manufacturing the(meth)acrylic polymer (I-a), (meth)acrylic acid esters and (meth)acrylicacid alkyl esters in which an alkyl group is substituted by a functionalgroup (such as a carboxyl group and a hydroxyl group) are preferablyused. With respect to the (meth)acrylic acid alkyl esters, examplesthereof include: ethyl(meth)acrylate, propyl(meth)acrylate,butyl(meth)acrylate, amyl(meth)acrylate, hexyl(meth)acrylate,octyl(meth)acrylate, nonyl(meth)acrylate, decyl(meth)acrylate,lauryl(meth)acrylate, tridecyl(meth)acrylate, myristyl(meth)acrylate andstearyl(meth)acrylate. With respect to the above-mentioned (meth)acrylicacid alkyl esters, not limited to those having a straight-chain (normal)alkyl group, those having a branched chain alkyl group may be used, and,for example, those having an iso-type or those in which an alkyl groupis substituted by a lower alkyl group (for example, an alkyl grouphaving 1 to 3 carbon atoms) [for example, ethylhexyl(meth)acrylate] maybe used.

Among these, in order to improve the flexibility of the cured product(thermal conductive material) of the resin composition, (meth)acrylicacid esters in which the number of carbon atoms in the alkyl groupmoiety (when substituted by a lower alkyl group, the total number ofcarbon atoms) is in a range of about 2 to 18 (more preferably, about 3to 15) are preferably used. Each of these monomers may be used alone, ora plurality of these may be used in combination. In the case when aplurality of these monomers are combined with one another, a pluralityof (meth)acrylic acid alkyl esters may be combined, and, for example,(meth)acrylic acid alkyl esters may be used in combination with(meth)acrylate containing a functional group, such ashydroxyethyl(meth)acrylate and (meth)acrylic acid. When such(meth)acrylate containing a functional group is used, the resulting(meth)acrylic polymer (I-a) is allowed to have improved wettability andthe like to the thermal conductive filler (III). The (meth)acrylicpolymer (I-a) obtained by using such (meth)acrylate containing afunctional group may be referred to as a crosslinking polymer (I-b),which will be described later; however, since the functional groupshould not be consumed by the crosslinkage or the like in order to exertwettability improving effects and the like, a crosslinking agent (VI) isnot added to the resin composition using the (meth)acrylic polymer(I-a).

Upon manufacturing the (meth)acrylic polymer (I-a), it is preferable touse 50 mass % or more of (meth)acrylic acid alkyl esters with the numberof carbon atoms in the alkyl group being in a range of 2 to 18 relativeto 100% by mass of the monomer component constituting the (meth)acrylicpolymer (I-a); it is more preferable to use 70 mass % or more thereof,and it is most preferable to use 80 mass % or more thereof. Thus, itbecomes possible to improve the flexibility of the thermal conductivematerial after the curing process, and also to improve theheat-transmitting area and the follow-up property to a subject to beattached. Moreover, since the amount of use of the plasticizer isreduced, it also becomes possible to prevent the plasticizer frombleeding out.

The glass transition point of the (meth)acrylic polymer (I-a) ispreferably set to 0° C. or less, more preferably to −30° C. or less,still more preferably to −40° C. or less. When the glass transitionpoint exceeds 0° C., the resulting cured product of the resincomposition tends to have insufficient flexibility. Here, the glasstransition point of the (meth)acrylic polymer (I-a) can be measuredthrough a commonly-used method by using a differential scanningcalorimeter.

With respect to the molecular weight of the (meth)acrylic polymer (I-a),the weight-average molecular weight, obtained by the gel-permeationchromatography (GPC) method on the basis of calibration withpolystyrene, is preferably set in a range from 10,000 to 1,000,000, morepreferably, from 30,000 to 800,000, most preferably, from 50,000 to500,000. When the weight-average molecular weight is less than 10,000,the resulting cured product of the resin composition has degradation inperformances such as a solvent-resistant property and a heat-resistantproperty, and, in contrast, the weight-average molecular weightexceeding 1,000,000 may cause high viscosity of the resulting(meth)acrylic polymer (I-a), resulting in a problem with the operabilityupon molding the resin composition.

In the case when the polymer (I) corresponds to the (meth)acrylicpolymer (I-a), the resin composition is preferably allowed to contain apolymerizable monomer (IV). Thus, the viscosity of the resin compositionis lowered so that the moldability is enhanced. This polymerizablemonomer (IV) is polymerized by a radical polymerization initiator (V)that is added thereto prior to the curing process of the resincomposition so that it functions so as to cure the resin composition.

Supposing that the total of the (meth)acrylic polymer (I-a) andpolymerizable monomer (IV) is 100% by mass, it is preferable to adjustthe (meth)acrylic polymer (I-a) to a range from 10 to 80% by mass, withthe polymerizable monomer (IV) being set in a range from 20 to 90% bymass. The ratio is more preferably set in a range from 15 to 70% by massfor the (meth)acrylic polymer (I-a) with the polymerizable monomer (IV)being set in a range from 30 to 85% by mass, and the ratio is mostpreferably set in a range from 30 to 60% by mass for the (meth)acrylicpolymer (I-a) with the polymerizable monomer (IV) being set in a rangefrom 40 to 70% by mass. In the case when the (meth)acrylic polymer isless than 10% by mass, that is, when the polymerizable monomer (IV)exceeds 90% by mass, for example, upon pre-forming into a sheet shape orupon molding, after the kneading process with a thermal conductivefiller, a separation undesirably tends to occur between the resin andthe thermal conductive filler, failing to provide a desirable method; incontrast, in the case when the (meth)acrylic polymer exceeds 80% bymass, that is, when the polymerizable monomer (IV) is less than 20% bymass, the viscosity of the resin composition becomes too high,undesirably resulting in deterioration in operability, degradation inthe surface smoothness of the resulting sheet after the performingprocess and degradation in surface smoothness upon molding.

With respect to the polymerizable monomer (IV), although notparticularly limited as long as it is a monomer having one radicalpolymerizable double bond, among those, (meth)acrylic acid alkyl estershaving an alkyl group with carbon atoms of 2 to 18,, which have beenexemplified as a monomer to be used upon manufacturing the (meth)acrylicpolymer (I-a), are preferably used. Two kinds or more of these may beused in combination. The amount of use of the (meth)acrylic acid alkylesters having an alkyl group with carbon atoms of 2 to 18 is preferablyset to 80% by mass or more in 100% by mass of the polymerizable monomer(IV) component.

If necessary, a monomer (hereinafter, referred to as “polyfunctionalmonomer”) that has two or more radical polymerizable double bonds in onemolecule may be used in one portion of the polymerizable monomer (IV).By using the polyfunctional monomer, it becomes possible to obtain acured product that is superior in heat resistance, chemical resistanceand creep property; therefore, the use thereof is desirably determineddepending on required performances of the cured product. Supposing thatthe total of the (meth)acrylic polymer (I-a) and polymerizable monomer(IV) is 100 parts by mass, the amount of use of the polyfunctionalmonomer is preferably set to 5 parts by mass or less, more preferably,to 4 parts by mass or less, still more preferably, to 3 parts by mass.When the amount of the polyfunctional 5 monomer exceeds 5 parts by mass,the resulting cured product of the resin composition may become poor inits flexibility.

Specific examples of the polyfunctional monomer include a polyfunctional(meth)acrylic monomer, divinyl benzene, diallyl phthalate and triallylcyanurate. Examples of the polyfunctional (meth)acrylic monomer include:di(meth)acrylates (preferably, C₂-s alkanediol di(meth)acrylate), suchas (poly)ethyleneglycol di(meth)acrylate, (poly)propyleneglycoldi(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentylglycoldi(meth)acrylate and 1,6-hexanediol di(meth)acrylate; tri(meth)acrylatessuch as trimethylol propane tri(meth)acrylate; tetra(meth)acrylates suchas pentaerythritol tetra(meth)acrylate; and condensates of theabove-mentioned di, tri and/or tetra(meth)acrylates, such asdipentaerythritol hexa(meth)acrylate. Each of the above-mentionedpolyfunctional polymerizable monomers may be used alone, or two or morekinds of them may be used in combination.

The above-mentioned (meth)acrylic polymer (I-a) can be obtained byallowing the above-mentioned material monomer to undergo a polymerizingreaction through a known radical polymerization method, such as bulkpolymerization, solution polymerization and emulsion polymerization. Inthe bulk polymerization method, when a partial polymerization method inwhich the polymerization is stopped in the middle of the process isadopted, a mixture of the polymer (I-a) and the polymerizable monomer(IV) is obtained in one process so that it becomes possible to provide aconvenient method desirably. Of course, the polymerizable monomer (IV)may be added to this mixture in a separate manner so as to be adjusted.Moreover, by adopting the solution polymerization method or the emulsionpolymerization method, water content, solvents and the like areevaporated after the polymerization of the (meth)acrylic polymer (I-a)has been completed, and the polymerizable monomer (IV) may be addedthereto.

Moreover, the material monomer of the (meth)acrylic polymer (I-a) may bepolymerized in the presence of the liquid-state plasticizer (II). Thisprocess makes it possible to easily control the polymerization rate incomparison with the bulk polymerization, and also to prevent impuritiessuch as water content and solvents from entering the resin composition.In this case, after all the material monomer of the (meth)acrylicpolymer (I-a) has been polymerized, the polymerizable monomer (IV) maybe added thereto separately, and, if necessary, the liquid-stateplasticizer (II) may be further added thereto. Moreover, thepolymerization of the material monomer of the (meth)acrylic polymer(I-a) may be terminated in the middle of the polymerization process, andthis method makes it possible to obtain a mixture of the (meth)acrylicpolymer (I-a), the polymerizable monomer (IV) and the liquid-stateplasticizer (II) through one process. Of course, the polymerizablemonomer (IV) and the liquid-state plasticizer (II) may be added to thismixture in a separate manner so as to adjust the compounding ratio.

Upon polymerization, a radical polymerization initiator is used. Thisradical polymerization initiator may be the same as the radicalpolymerization initiator (V) that is added separately to the resincomposition containing the (meth)acrylic polymer (I-a) and thepolymerizable monomer (IV) and used for polymerizing the polymerizablemonomer (IV), or may be different therefrom; however, since thisinitiator is consumed through the polymerization reaction, thepolymerization initiator (V) is separately added to the resincomposition at an appropriate timing after the reaction.

With respect to the radical polymerization initiator (V), examplesthereof include thermal polymerization initiators and the like, such asan azo-based initiator and an organic peroxide, and each of these may beused alone or two or more kinds of these may be used in combination.

With respect to the azo-based initiator, examples thereof include:2,2′-azobisisobutyronitrile, dimethyl-2,2′-azobis(2-methyl propionates)and 2-phenylazo-2,4-dimethyl-4-methoxy valeronitrile.

With respect to the organic peroxide, examples thereof include: ketoneperoxides, such as methyl ethyl ketone peroxide; hydroperoxides, such ascumene hydroperoxide; diacyl peroxides, such as benzoyl peroxide andlauryl peroxide; dialkyl peroxides, such as dicumyl peroxide;peroxyketals, such as 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane;alkyl peresters, such as t-amylperoxy-2-ethylhexanate,t-butylperoxy-2-ethylhexanate, t-amylperoxy-3,5,5-trimethylhexanate,1,1,3,3-tetramethylbutylperoxy-2-ethylhexanate,1,1,3,3-tetramethylbutylperoxy-2-ethylhexanate,t-butylperoxy-3,5,5-trimethylhexanate and t-butylperoxy pivalate; andpercarbonates, such as t-butylperoxyisopropyl carbonate,t-butylperoxy-2-ethylhexyl carbonate, 1,6-bis(t-butylperoxycarbonyloxy)hexane.

Although not particularly limited as long as it allows (meth)acrylicacid esters to undergo a radical polymerization reaction, the amount ofuse of the radical polymerization initiator is appropriately setdepending on the kinds of the radical polymerization initiator, and withrespect to 100 parts by mass of the material monomer, it isapproximately set, for example, in a range of 0.01 to 1 part by mass,more preferably, 0.05 to 0.7 part by mass, most preferably, 0.10 to 0.5part by mass. Here, the radical polymerization initiator may beappropriately divided and then added, if necessary, or may be addedafter having been diluted by the liquid-state plasticizer (II).

Upon polymerization, a chain transfer agent may be added, if necessary.With respect to the chain transfer agent, various known chain transferagents may be used, and examples thereof include: a-methylstyrene dimer,carbon tetrachloride and thiol compounds (for example,n-dodecylmercaptan). The amount of use of the chain transfer agent isappropriately set on demand, and, for example, it is set in a range fromabout 0.01 to 2 parts by mass, more preferably, about 0.05 to 1.5 partsby mass, still more preferably, about 0.10 to 1 part by mass, withrespect to 100 parts by mass of the material monomer.

The reaction temperature may also be set on demand, and for example, itis set in a range from about 40 to 150° C., more preferably, about 50 to100° C., in most cases.

When the polymer (I) corresponds to the (meth)acrylic polymer (I-a), theradical polymerization initiator (V) is preferably contained in theresin composition together with the polymerizable monomer (IV). Thepresence of the polymerization initiator (V) makes it possible to curethe resin composition quicker to improve the productivity of the thermalconductive material. With respect to the radical polymerizationinitiator (V), in addition to the aforementioned conventionally knownthermal polymerization initiators, photo initiators and the like may beused. For example, upon curing the resin composition by using heat, thethermal polymerization initiator may be used, and upon curing the resincomposition by using ultraviolet rays, the photo initiator may be usedfor the curing process; thus, the initiator is appropriately selecteddepending on curing methods on demand. Of these methods, the method forcuring the resin composition by using heat is more preferable becauseits curing device is simpler, and superior from the viewpoint of costs,and it is more preferable to cure the resin composition by using athermal polymerization initiator. In order to accelerate the function ofthe thermal polymerization initiator, known curing accelerator andcuring acceleration assistant may be used. The amount of addition of thethermal polymerization initiator is preferably set in a range of 0.1 to5 parts by mass, the amount of the curing accelerator is set in a rangeof 00.5 to 3 parts by mass, and the amount of the curing accelerationassistant is set in a range of 0.05 to 2 parts by mass, with respect tothe total 100 parts by mass of the (meth)acrylic polymer (I-a) and thepolymerizable monomer (IV).

In the case when the polymer (I) corresponds to the (meth)acrylicpolymer (I-a), with respect to the resin composition, supposing that thetotal of the liquid-state plasticizer (II), the (meth)acrylic polymer(I-a) and polymerizable monomer (IV) is 100% by mass, it is preferableto adjust the liquid-state plasticizer (II) within a range of 5 to 60%by mass (more preferably, 15 to 40% by mass, the (meth)acrylic polymer(I-a) within a range of 10 to 60% by mass (more preferably, 10 to 50% bymass) and the polymerizable monomer (IV) within a range of 30 to 85% bymass (more preferably, 40 to 65% by mass).

In the case when the liquid-state plasticizer (II) is less than 5% bymass, the hardness of the resulting cured product of the resincomposition tends to become higher, failing to provide properflexibility required for the thermal conductive material, and in thecase when the liquid-state plasticizer (II) exceeds 60% by mass,although the resulting cured product of the resin composition hasimproved flexibility, the liquid-state plasticizer (II) tends to beseparated from the cured product.

In the case when the (meth)acrylic polymer (I-a) is less than 10% bymass, for example, upon molding the resulting resin composition into athermal conductive sheet (upon curing), a separation tends to occurbetween the resin and the other components, and in the case when the(meth)acrylic polymer (I-a) exceeds 60% by mass, the viscosity of theresulting resin composition tends to become too high, resulting indeterioration in operability and degradation in the surface smoothnessof the resulting sheet.

In the case when the polymerizable monomer (IV) is less than 30% bymass, the liquid-state plasticizer (II) tends to be separated from theresulting cured product of the resin composition, and in contrast, inthe case when the polymerizable monomer (IV) exceeds 85% by mass, theresin tends to be separated from the other components.

The following description will discuss the case in which the polymer (I)corresponds to the crosslinking polymer (I-b). The crosslinking polymer(I-b) is a polymer that has a functional group that is allowed to reactwith the crosslinking agent (VI) so that a cured product (thermalconductive material) is formed by crosslinking through the reaction withthe crosslinking agent (VI).

The crosslinking polymer (I-b) is obtained by copolymerizing apolymerizable monomer (I-b-1) with a polymerizable monomer (I-b-2)having a functional group used for a crosslinking process. Thepolymerizable monomer (I-b-1) is a polymerizable monomer having oneradical polymerizable unsaturated group in its molecule. This monomer(I-b-1) has no functional group capable of reacting with thecrosslinking agent (VI). Here, the polymerizable monomer (I-b-2) is amonomer having one functional group used for crosslinking and oneradical polymerizable unsaturated group in its molecule.

The polymerizable monomer (I-b-1) is not particularly limited as long asit is a monomer that contains one radical polymerizable unsaturatedgroup in its molecule. More specifically, (meth)acrylic acid alkylesters having an alkyl group with carbon atoms of 2 to 18 are preferablyused in the same manner as the polymerizable monomer (IV). The amount ofuse of the (meth)acrylic acid alkyl ester having an alkyl group withcarbon atoms of 2 to 18 is preferably set to 50% by mass or more, morepreferably, to 70% by mass or more, most preferably, to 80% by mass ormore, with respect to 100% by mass of the monomer components forming thecrosslinking polymer (I-b).

With respect to the functional group-containing polymerizable monomer(I-b-2), any monomer may be used as long as it contains one functionalgroup used for crosslinking and one radical polymerizable unsaturatedgroup in its molecule. With respect to the functional group, examplesthereof include: a carboxyl group, a hydroxyl group, a mercapto group, anitrile group, an amino group, an amide group, a carboxylic anhydridegroup, an epoxy group and an isocyanate group. Among these, the hydroxylgroup is preferably used. With respect to specific hydroxyl groupcontaining monomers, examples thereof include:2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate,2-hydroxybutyl(meth)acrylate, polyethyleneglycol mono(meth)acrylate,polypropyleneglycol(meth)acrylate, glycerin(meth)acrylate andhydroxystyrene.

In the case when the polymerizable monomer (I-b-1) and the functionalgroup-containing polymerizable monomer (I-b-2) are polymerized with eachother, the rate of the functional group-containing polymerizable monomer(I-b-2) is preferably set in a range from 0.01 to 5 mole %, morepreferably, from 0.1 to 4 mole %, most preferably, from 0.3 to 3 mole %,with respect to the total 100 mole % of the two components. When thefunctional group-containing polymerizable monomer (I-b-2) exceeds 5 mole%, the resulting cured product (thermal conductive material) may havedeterioration in its flexibility, and when it is less than 0.01 mole %,the liquid-state plasticizer (II) is not held in the cured product afterthe crosslinking process, sometimes failing to form a gel state.

The glass transition point of the crosslinking polymer (I-b) ispreferably set to 0° C. or less, more preferably, to −20° C. or less,still more preferably, to −30° C. or less. When the glass transitionpoint exceeds 0° C., the resulting resin composition may fail to havesufficient flexibility.

With respect to the molecular weight of the crosslinking (meth)acrylicpolymer (I-b), the mass-average molecular weight (Mw), obtained by thegel-permeation chromatography (GPC) method on the basis of calibrationwith polystyrene, is preferably set in a range from 50,000 to 2,000,000,more preferably, from 80,000 to 1,500,000, most preferably, from 100,000to 1,000,000. When the mass-average molecular weight Mw is less than50,000, it takes a long time to obtain the cured product, and it becomesdifficult for the cured product to form a gel-state resin. In contrast,Mw exceeding 2,000,000 may cause a high viscosity in the resincomposition, resulting in a problem with the operability.

The crosslinking polymer (I-b) can be manufactured by using the samemethod as the synthesis method of the aforementioned (meth)acrylicpolymer (I-a). Moreover, it can also be synthesized in the liquid-stateplasticizer (II). Here, it is not necessary for the crosslinking polymer(I-b) to be partially polymerized and the polymerization reaction is tobe completed.

With respect to the crosslinking agent (VI), any compound may be used aslong as it has two or more functional groups used for crosslinking inits molecule, without having a radical polymerizable unsaturated group,and it is selected on demand depending on the functional group possessedby the crosslinking polymer (I-b), that is, on the kinds of thefunctional group of the functional group-containing polymerizablemonomer (I-b-2). For example, when the crosslinking polymer (I-b) isobtained by using a monomer having a hydroxyl group as the functionalgroup-containing polymerizable monomer (I-b-2), those compounds havingtwo or more isocyanate groups in the molecule are preferably used as thecrosslinking agent (VI). Examples thereof include: hexamethylenediisocyanate, isophorone diisocyanate, p-phenylene diisocyanate,2,6-toluene diisocyanate, 2,4-toluene diisocyanate,bis(4-isocyanatecyclohexyl) methane, a trimethylolpropane adduct oftoluene diisocyanate, an isocyanurate modified form of toluenediisocyanate, an HDI-based oligomer, an isocyanurate modified form, abiuret-modified form and a uretodione form of HDI, and an isocyanuratemodified form of IPDI. Only one kind of these may be used, or two ormore kinds of these may be used in combination. Moreover, the isocyanategroup in the crosslinking agent (VI) may be blocked by c-caprolactum,butanone oxium or phenol. Here, an isocyanate-group-containing(co)polymer, which is obtained by (co)polymerizing a monomer having anisocyanate group with another monomer, if necessary, may be used as thecrosslinking agent (VI), and in this case, the (co)polymer is preferablyallowed to have a mass-average molecular weight of 500,000 or less andto be in a liquid-state at 25° C., with a viscosity of 8000 mPa·s orless. With respect to the monomer having an isocyanate group, examplesthereof include 2-methacryloyloxyethyl isocyanate, methacryloylisocyanate and the like; however, the monomer is not particularlylimited to these. Only one kind of the isocyanate-containing monomer maybe used, or two or more kinds of these may be used in combination.Moreover, the isocyanate group in the monomer may also be blocked.

The crosslinking agent (VI) is set in a range from 0.1 equivalents ormore (more preferably, 0.5 equivalents or more, most preferably, 0.7equivalents or more) to 2.0 equivalents or less (more preferably, 1.8equivalents or less, still more preferably, 1.5 equivalents or less)with respect to 1 equivalent of the functional group of the crosslinkingpolymer (I-b).

A preferable combination between the functional group of the functionalgroup-containing polymerizable monomer (I-b-2) and the functional groupof the crosslinking agent (VI) is formed between at least one functionalgroup selected from the group consisting of a carboxyl group, a hydroxylgroup, a mercapto group, an amino group and an amide group and at leastone functional group selected from the group consisting of a carboxylicanhydride group, an epoxy group and an isocyanate group. The combinationof the functional group-containing-polymerizable monomer (I-b-2) and thecrosslinking agent (VI) is appropriately determined based upon theabove-mentioned combinations so that unreacted functional groups in theresulting cured product can be reduced.

The most preferable combination is a combination between the functionalgroup-containing polymerizable monomer (I-b-2) having a hydroxyl groupand the crosslinking agent (VI) having an isocyanate group. By usingthis combination, the curing reaction can be carried out at a lowertemperature in a shorter period of time, making it possible to achieve areaction that is superior in economical efficiency.

In the case when the polymer (I) corresponds to the crosslinking polymer(I-b), the resin composition preferably contains a crosslinkingaccelerator or crosslinking acceleration assistant used for acceleratingthe crosslinking reaction. In particular, when the functionalgroup-containing polymerizable monomer (I-b-2) having a hydroxyl groupand the crosslinking agent (VI) having an isocyanate group are combinedwith each other, the reaction is preferably carried out by using anorganic metal compound as the crosslinking accelerator. With respect tothe organic metal compound, any organic metal compound may be used aslong as it has a transition metal element belonging to 3A to 7A, 8 and1B groups and a metal element belonging to 2B to 6B in the PeriodicTable described in Chemistry Handbook Application 3^(rd) Revised Edition(edited by Japan Chemical Society, published by Maruzen Co., Ltd.), andit is selected on demand depending on the reaction time, the reactiontemperature, the composition of the resin composition and the like.Among these, compounds of tin, zinc or lead are preferably used, and tincompounds are more preferably used. Only one kind of these organic metalcompounds may be used, or two or more kinds of these may be used incombination. Specific examples thereof include: organic tin compounds,such as dibutyltin dilaurate, dibutyltin diacetate, dibutyltindi(2-ethylhexanoate), dihexyltin diacetate, dioctyltin dilaurate,dimethyltin bis(isooctyl thioglycolic acid ester)salt and tin octylate;organic zinc compounds, such as zinc naphthenate and 2-ethylhexyl zinc;and organic lead compounds, such as lead stearate, lead naphthenate and2-ethylhexyl lead.

Moreover, upon carrying out a crosslinking reaction, the crosslinkingaccelerator of this type is preferably used in combination with acompound having an atom with a pair of isolated electrons in itsmolecule. Consequently, this compound having an atom with a pair ofisolated electrons in its molecule is preferably blended in the resincomposition. This is because the inventors of the present invention havefound the phenomenon that, when an accelerated test in which a thermalconductive sheet made of the resin cured product of this type has beenheld under high temperature for a long time is carried out, the sheethardness is lowered, and also found that in order to suppress thephenomenon, it is effective to combindly use the above-mentioned organicmetal compound and the compound having an atom with a pair of isolatedelectrons in its molecule, upon carrying out the crosslinking process.Presumably, the sheet hardness is lowered because molecular chains ofthe crosslinking polymer, which have been swollen by the liquid-stateplasticizer (II), are exposed to high temperatures, with the result thatthe crosslinking bonds come off, however, when there is a compoundhaving a pair of isolated electrons that can be coordinate-bonded to ametal atom, the dissociation of crosslinking bonds can be preventedalthough the reason for this has not been clarified. Thishardness-reduction preventive mechanism is exerted not only on agel-state resin containing a thermal conductive filler such as a thermalconductive sheet, but also on a gel-state resin containing no thermalconductive filler or the like, in the same manner. Consequently, in thecase when such a polyurethane-based gel-state resin is applied to thefield that is subjected to high temperature, it is preferable to carryout a urethane-forming reaction in the presence of an organic metalcompound and a compound having an atom with a pair of isolated electronsin its molecule, in order to improve the heat resistance.

With respect to the compound having an atom with a pair of isolatedelectrons in its molecule, a compound having a nitrogen atom or anoxygen atom with a pair of isolated electrons in its molecule ispreferably used, and in particular, a compound having two or more atoms,each having a pair of isolated electrons, in its molecule is morepreferably used. Specific examples thereof include: tertiary aminecompounds, such as N,N,N′,N′-tetramethyl-1,6-hexane diamine,N,N,N′-triethylaminoethyl methanol amine, N,N,N′-trimethylaminoethylethanol amine and hexamethylphosphor amide, and ketone compounds, suchas acetyl acetone. Two or more kinds of these may be used incombination.

The amount of use of the organic metal compound serving as acrosslinking accelerator is preferably set in a range of 0.001 to 3parts by mass with respect to 100 parts by mass of the crosslinkingpolymer (I-b), and the ratio (mass ratio) between the organic metalcompound and the compound having an atom with a pair of isolatedelectrons in its molecule is preferably set in a range of 1/1 to 1/100.

The resin compound containing the crosslinking polymer (I-b) may containan acidic compound. This acidic compound, for example, allows thethermal conductive filler and the like to be quickly dispersed uniformlyso that it functions to improve the productivity. Moreover, it alsomakes the viscosity of the resin composition lower so that a largeamount of the thermal conductive filler and the like can be blended,making it possible to improve the heat-radiating (thermal conductive)performance of the resulting cured product. Moreover, it also becomespossible to easily remove air that is contained upon manufacturing theresin composition. In this manner, the acidic compound allows thethermal conductive filler that is essential as the thermal conductivematerial to exert its effects to the maximum level.

With respect to the acidic compound, not particularly limited, anycompound may be used as long as it exerts acidity of 1.0 or more in PKa(acid dissociation constant) defined in Chemistry Handbook Basics II(edited by the Chemical Society of Japan, published by Maruzen Co.,Ltd.), and in order to fully exert the effects of the present invention,an organic acidic compound is preferably used, and carboxylic acid ismore preferably used. Moreover, in order to prevent corrosion onelectric and electronic parts and the like caused by the acidic compoundin the cured product of the resin composition, the acidic compoundshould be evaporated from the cured product after the cured product hasbeen obtained; therefore, carboxylic acid which has a boiling point of250° C. or less under normal pressure is preferably used. Carboxylicacids of this type corresponds to carboxylic acids having carbon atomsthe total number of which is from 1 to 8. Moreover, this includessubstituted forms, and one kind thereof may be used, or two or morekinds of these may be used in combination.

With respect to carboxylic acid having a boiling point of 250° C. orless and carbon atoms the total number of which is in a range from 1 to8, examples thereof include formic acid, acetic acid, propionic acid,butanoic acid, valeric acid, hexanoic acid and 2-ethylhexanoic acid.When the curing temperature is 130° C. or less, it is preferable to usecarboxylic acid in which the boiling temperature under normal pressureof the acidic substance to be used is 170° C. or less.

In the resin composition, the acidic compound is preferably contained at0.005 parts by mass or more (more preferably, 0.01 parts by mass ormore, most preferably, 0.03 parts by mass or more) with respect to 100parts by mass of the crosslinking polymer (I-b). Here, the upper limitvalue is preferably set to about 5 parts by mass, more preferably, toabout 3 parts by mass, most preferably, to about 2 parts by mass. Bysetting the lower limit value and the upper limit value to theabove-mentioned values, the blending effects of the acidic compound areappropriately exerted.

In the case of the resin composition in which the polymer (I)corresponds to the crosslinking polymer (I-b), supposing that the totalamount of the two components is 100% by mass, the ratio between theliquid-state plasticizer (II) and the crosslinking polymer (I-b) ispreferably set so that the liquid-state plasticizer (II) is in a rangefrom 50 to 90% by mass (more preferably, from 50 to 80% by mass, mostpreferably, from 55 to 80% by mass), while the crosslinking polymer(I-b) is in a range from 10 to 50% by mass (more preferably, from 20 to50% by mass, most preferably, from 20 to 45% by mass).

When the liquid-state plasticizer (II) exceeds 90% by mass, that is,when the crosslinking polymer (I-b) is less than 10% by mass, theliquid-state plasticizer is not held in the cured product sufficientlyto fail to form a gel state in some cases. Consequently, stickinesstends to occur on the resulting cured product which has been obtained byextruding the resin composition into a sheet form after kneading withthe thermal conductive filler, degradation tends to occur in the surfacesmoothness of the sheet and a separation between the resin and thethermal conductive filler tends to occur, failing to provide apreferable process. In contrast, when the crosslinking polymer (I-b)exceeds 50% by mass, that is, when the liquid-state plasticizer (II) isless than 50% by mass, the viscosity of the resin composition becomeshigher to sometimes cause deterioration in the operability and the likeand a reduction in the flexibility of the resulting cured product.

The resin composition of the present invention contains a thermalconductive filler (III) having a thermal conductivity of 20 W/m·K ormore as an essential component. Specific examples thereof includeinorganic fillers (oxides such as aluminum oxide, magnesium oxide, zincoxide and silicon oxide; hydroxides such as aluminum hydroxide andmagnesium hydroxide; carbides such as silicon carbide; and nitrides suchas aluminum nitride, boron nitride and silicon nitride, etc.),metal-based fillers [silver, copper, aluminum, iron, zinc, nickel, tinand alloys of these (for example, copper-tin alloy, etc.)], andcarbon-based fillers (carbon, graphite, etc.). In the applications thatrequire a high-level electrical insulating property, inorganic fillersare preferably used. When used, two or more kinds of these may be usedin combination. The thermal conductivity of the thermal conductivefiller to be used can be measured on its sintered product by using athermal conductivity measuring device using a hot disk method: Item No.TPA-501, made by Kyoto Electronics Manufacturing Co., Ltd.

The thermal conductive filler (III) of this type having a thermalconductivity of 20 W/m·K or more is preferably contained in a range of100 to 1500 parts by mass, more preferably, 200 to 1300 parts by mass,with respect to 100 parts by mass of the polymer (I). As the amount ofcharge of the thermal conductive filler to the polymer (I) increases,the thermal conductivity of the resulting cured product (thermalconductive material) becomes higher, making it possible to improve theheat-radiating performance. In contrast, since the resulting curedproduct tends to have deterioration in the flexibility, the amount ofcharge is preferably adjusted by taking a required thermal conductivityand the flexibility of the cured product into consideration. The thermalconductive filler (III) may be subjected to a surface treatment, such asa silane treatment, if necessary, in order to enhance the dispersibilityin the composition and increase the amount of charge. Moreover, withrespect to the shape of the thermal conductive filler (III), notparticularly limited, examples thereof include a spherical shape, afiber shape, a scale shape, a flat shape, a fragmental shape and anamorphous shape.

In the resin composition of the present invention, in order to improvethe strength and handling property of the resulting cured product, thesurface of the molded product of the resin composition may beimpregnated or adhered with a resin, inorganic fibers or organic fibers.Moreover, with respect to the resin composition of the presentinvention, any of conventionally known materials in the molding materialfield and the like such as reinforced fibers, an inorganic or organicfiller, a polymerization initiator, a polymerization inhibitor, a lowcontraction agent, a releasing agent, a thickener, an antifoamer, athixotropic agent, a ultraviolet-ray absorbing agent, a ultraviolet-raystabilizer, an antioxidant, a flame retarder, a coupling agent,pigments, dyes, a magnetic material, an antistatic agent, anelectromagnetic wave absorbing agent, paste-state oil, paraffin wax,microcrystalline wax, higher fatty oil and a thermo-softener, may beapplicable, unless the objectives of the present invention areintervened.

The degree of additions of these is preferably determined to an amountthat would not impair the objectives of the present invention, andspecifically, the amount is preferable set to 1000 parts by mass or lessas the total amount of the additives, with respect to 100 parts by massof the polymer (I). The upper limit of the amount of addition ispreferably set to 900 parts by mass, more preferably, to 800 parts bymass.

The resin composition of the present invention, which is in a liquidstate at normal temperature, can be obtained by using a conventionallyknown kneader. Although not particularly limited, examples thereofinclude continuous kneaders, such as a mixer, a roll mill, a Van Ballymixer, a kneader, a pressurized kneader and a twin-screw kneader.Moreover, the kneading process may be carried out, while the innerpressure of the device is being decompressed to remove air contained inthe composition, or a heating process and/or a pressurizing process arebeing carried out, if necessary. When the kneading process, thesucceeding molding process and the like are taken into consideration, itis preferable to adjust the viscosity of the resin composition prior tothe addition of the thermal conductive filler (III) to 5000 mPa·s orless (more preferably, 3000 mPa·s or less, still more preferably, 2200mPa·s or less) at 25° C.

Here, in order to prevent curing of the resin composition of the presentinvention during storage, it is preferable to store the constituentcomponents of the resin composition separately. When the polymer (I)corresponds to the (meth)acrylic polymer (I-a), for example, theconstituent components are preferably separated into a first materialthat contains the (meth)acrylic polymer (I-a) and the polymerizablemonomer (IV), without containing the radical polymerization initiator(V), and a second material that contains the radical polymerizationinitiator (V), without containing the polymerizable monomer (IV). Theliquid-state plasticizer (II) is preferably put into the first materialor the second material, or both of these materials with the liquid-stateplasticizer divided in an appropriate ratio. In contrast, when thepolymer (I) corresponds to the crosslinking polymer (I-b), thecrosslinking polymer (I-b) and the crosslinking agent (VI) arepreferably stored separatly. Therefore, for example, a mixture of theliquid-state plasticizer (II) and the crosslinking polymer (I-b) ispreferably prepared as a first material, and the crosslinking agent (VI)is preferably prepared as a second material. Preferably, thecrosslinking accelerator, the compound having an atom with a pair ofisolated electrons in its molecule, the acidic compound and the like arepreliminarily blended into either the first material or the secondmaterial, or both of the materials. In any of the above-mentioned cases,since the viscosity of the mixture becomes higher when the thermalconductive filler (III) is kneaded, the thermal conductive filler (III)is preferably kneaded prior to the molding process, from the view pointof operability.

The resin composition of the present invention is cured so that thethermal conductive material can be obtained. In the case when thepolymer (I) corresponds to the (meth)acrylic polymer (I-a), the resincomposition is cured by a polymerization reaction of the polymerizablemonomer (IV) in the composition, and in the case when the polymer (I)corresponds to the crosslinking polymer (I-b), the resin composition iscured by a crosslinking reaction with the crosslinking agent (VI) toform a thermal conductive material. Moreover, since the liquid-stateplasticizer (II) is held in three-dimensional network of high molecularchains, it is possible to obtain a gel-state cured product that isflexible and superior in heat resistance, and consequently to provide asuperior thermal conductivity. With respect to the heating temperatureat the time of curing, in the case of the polymerization reaction,although not particularly limited, it is set to a temperature higherthan a 10-hour half-life period temperature of the radicalpolymerization initiator (V) by 10 to 50° C., and in the case of thecrosslinking reaction, a temperature that is suitable for thecrosslinking agent is selected so that it becomes possible to increasethe curing rate, and consequently to improve the productivity.

The resin composition of the present invention may be formed into adesired shape, and the shape and the molding method are not particularlylimited. For example, the resin composition may be charged into aninjection molding mold or a batch-type mold so as to be molded into adesired shape, or may be formed into a sheet shape by using an extruderor a method such as casting. The sheet-shaped product is effectivelyused as a thermal conductive sheet.

Moreover, the molding process may be carried out while conducting aheating process in order to simultaneously mold the resin compositioninto a thermal conductive material having a desired shape, whileaccelerating the polymerization reaction and crosslinking reaction.Furthermore, the resin composition may be once molded into a desiredshape, and then heated or aged (maintained at room temperature for along time) so that the liquid-state plasticizer (II) is spread over theinside of the crosslinking polymer to form a gel-state resin.

The thermal conductive material of the present invention may be obtainedby allowing the polymerizable monomer (IV) containing a polyfunctionalmonomer in a range of 0.01 to 5% by mass to undergo a polymerizationprocess in the presence of the liquid-state plasticizer (II) and thethermal conductive filler (III), without using the polymer (I).

The thermal conductive material, obtained by curing the resincomposition of the present invention, is preferably designed to havehardness in a range of 5 to 60. This hardness is defined as a valuemeasured at 25° C. by using an Asker rubber C-type hardness tester, madeby Koubunshi Keiki Co., Ltd. Here, in the case when a cured product,obtained without adding the thermal conductive filler to the resincomposition, is set to hardness in a range of 5 to 80, it becomespossible to obtain a thermal conductive material that is set in theabove-mentioned hardness range. Here, this hardness is defined as avalue measured at 25° C. by using an Asker rubber F-type hardnesstester, made by Koubunshi Keiki Co., Ltd. With respect to the hardness,a pressing stylus of the hardness tester is pushed into the center of adisc shaped sample having a thickness of 15 mm and a diameter in a rangefrom 5 to 8 cm; thus, the pressing face is made in close-contact withthe sample so that the maximum indicated value within a second from thetime of the close-contact is used as the hardness.

Preferably, the thermal conductive material of the present invention iscapable of exerting flexibility stably for a long time. Thedetermination as to whether or not the long-term flexibility has beenachieved is made by checking for whether or not the liquid-stateplasticizer (II) has been evaporated; therefore, the mass loss rate (%),obtained when the thermal conductive material has been maintained in anoven heated to 130° C. (or alternatively to 100° C.) for 168 hours, canbe used as its guideline, and the mass loss rate is preferably set to 5%or less, more preferably, to 3% or less, still more preferably, to 2% orless.

EXAMPLES

The following description will discuss the present invention in detailby means of examples; however, the present invention is not intended tobe limited by these examples, and it will be obvious that the same maybe varied in many ways. All such variations and modifications are not tobe regarded as a departure from the technical scope of the invention. Inthe Examples and Comparative Examples, “parts” refers to “parts by mass”and “%” refers to “% by mass”, unless otherwise indicated.

Experiment 1 (Experiments Relating to a Resin Composition in whichPolymer (I) is a (meth)acrylic Polymer (I-a)) Synthesis Example 1

Into a container equipped with a thermometer, a stirring device, a gasintroducing pipe, a reflux condenser and a dropping funnel were charged40 parts of 2-ethylhexyl acrylate (2EHA), 50 parts of toluene and 0.3parts of α-methylstyrene serving as a chain transfer agent, and theinner gas of the container was replaced with a nitrogen gas. This washeated to 80° C., and a mixture of 0.05 parts of azoisobutyronitrileserving as a polymerization initiator and 10 parts of toluene wascharged into the dropping funnel, and dropped into the container in twohours. To this was further added 0.01 parts of azoisobutyronitrile, andthe resulting mixture was heated to 90° C. and allowed to undergo apolymerization reaction for 3 hours. Prior to the completion of thepolymerization reaction, air was blown thereto to cool the system sothat the polymerization was completed; thus, a mixture ofpoly-2-ethylhexyl acrylate (PEHA) and toluene was obtained. Next, thepressure of the system was reduced to distill off toluene so that PEHAwas obtained. With respect to the molecular weight of this PEHA measuredby GPC (Gel Permeation Chromatography), the weight-average molecularweight Mw was 106,000 and the number-average molecular weight Mn was51,000. Moreover, the glass transition point temperature, measured by adifferential scanning calorimeter according to a conventional method,was −60° C.

Synthesis Example 2

Into a container equipped with a thermometer, a stirring device, a gasintroducing pipe, and a reflux condenser was charged 100 parts of laurylmethacrylate (LMA), and the inner gas of the container was replaced witha nitrogen gas. This was heated to 80° C., and a mixture of 0.02 partsof mercaptopropionic acid as a chain transfer agent and 0.01 parts ofazoisobutyronitrile serving as a polymerization initiator were addedthereto, and the resulting mixture was allowed to undergo a bulkpolymerization reaction for 3.0 hours under nitrogen atmosphere. Priorto the completion of the polymerization reaction, simultaneously as airwas blown thereto, 0.1 parts of a polymerization inhibitor, that is,hydroquinone, was added thereto, and the system was then cooled toterminate the polymerization reaction in the middle of the process. Inthe resulting mixture, polylauryl methacrylate (PLMA) was 50.0%, andLMA, which was a polymerizable monomer (IV) component, was 50.0%. Theviscosity of the resulting PLMA at 25° C. was 4980 mPa·s. With respectto the molecular weight of this PLMA measured by GPC, the weight-averagemolecular weight Mw was 136,000 and the number-average molecular weightMn was 58,000. Moreover, the glass transition point temperature,measured by a differential scanning calorimeter according to aconventional method, was −65° C.

No.1-1

To a mixture (100 parts) composed of 30 parts of PEHA, 39 parts of LMAserving as a monomer, 1 part of polyethylene glycol dimethacrylate (madeby Kyoei Chemical Co., Ltd. tradename: “Light Ester 9EG”) serving as apolyfunctional monomer, 30 parts of trimellitic acid ester-basedliquid-state plasticizer (made by Asahi Denka Co., Ltd., tradename:“ADK-Cizer C880”) (hereinafter, this mixture prior to adding apolymerization initiator thereto, is sometimes referred to as“liquid-state resin”) was added 1 part of 1,1,3,3-tetramethylbutylperoxy2-ethyl hexanoate (made by Kayaku Akzo Corporation: tradename:“Kayaester TMPO-70”) serving as a thermal polymerization initiator, andthe resulting mixture that had been defoamed was poured into a glasscell having a PET film with a thickness of 15 mm, which has beensubjected to a releasing treatment, and this was allowed to undergo apolymerization reaction in an oven at 80° C. for one hour and, further,at 100° C. for one hour so that a plate-shaped cured product wasobtained. The resulting cured product was subjected tohardness-measurement under the following criteria, and the results areshown in Table 2. Here, when 3 g of the liquid-state plasticizer (theabove-mentioned “ADK-Cizer C880”) was put into a watch glass having 5 cmin diameter, made of aluminum, and held in an oven heated to 130° C. for24 hours, the mass loss rate thereof was 0.07%. Moreover, the viscositythereof at 25° C. was 100 mPa·s and the solidifying point thereof was−21° C.

Next, 100 parts of the liquid-state resin, 1 part of the above-mentioned“Kayaster TMPO-70” serving as a thermal polymerization initiator, 0.1parts of an antifoamer (made by BYK-Chemie Japan KK: tradename “A-515”)and 400 parts of aluminum oxide having a thermal conductivity of 30W/m·K (made by Showa Denko K.K.: item number AS-10) were uniformlykneaded to prepare a resin composition for a thermal conductivematerial. Thereafter, the resin composition was subjected to a defoamingprocess, and poured into a glass cell having a PET film with a thicknessof 1 mm, which had been subjected to a releasing treatment, and furtherpolymerized in an oven at 80° C. for one hour, and then at 100° C. forone hour to be cured. The resulting sheet-shaped cured product wasevaluated based upon the following criteria, and the results are shownin Table 2.

[Hardness of the Plate-shaped Cured Product]

As described above, to 100 parts of the liquid-state resin was added 1part of the above-mentioned “Kayaster TMPO-70” serving as a thermalpolymerization initiator, and the resulting mixture that had beendefoamed was poured into a container with a thickness of 15 mm, and themixture was heated in an oven at 80° C. for one hour and, further, at100° C. for one hour so that the mixture was cured. An Asker rubberF-type hardness tester, made by Koubunshi Keiki Co., Ltd., was put inthe center of the measuring sample, with a pressing stylus of thehardness tester being pushed into the center of the sample cut into adisc-shape with a thickness of 15 mm and a diameter in a range of 5 to 8cm; thus, the pressing face was made in close-contact with the sample sothat the maximum indicated value within a second from the time of theclose-contact was used as the hardness. The measurements were carriedout at 25° C.

[Moldability of Sheet]

The sheet-shaped cured product obtained as described above was visuallyobserved, and evaluated based upon the following criteria.

-   ◯: Neither irregularities nor bubbles were found on the sheet    surface, and the surface was uniform without a separation between    the resin and the inorganic filler so that a desired surface    property was obtained.-   X: Irregularities and bubbles were found on the sheet surface. A    separation occurred between the resin and the inorganic filler, with    the result that an uneven sheet was produced.    [Initial Thermal Conductivity of Sheet]

The thermal conductivity of the sheet was measured by using a QuickThermal Conductivity Meter, Model QTM-500, available from KyotoElectronics Manufacturing Co., Ltd. With respect to the measuringsample, a sheet-shaped cured product, laminated to a thickness of 10 mm,was used. The measurements were carried out at 25° C.

[Initial Hardness of Sheet]

The initial hardness of the sheet was measured by using an Asker rubberC-type hardness tester made by Koubunshi Keiki Co., Ltd., in compliancewith JIS K7312. With respect to the measuring sample, a sheet-shapedcured product, laminated to a thickness of 10 mm, was used, and in thesame manner as the use of F-type hardness tester, the measurements werecarried out at 25° C. The smaller the resulting numeric value, the moreflexible the sheet becomes.

[Heat Resistant Property]

After the sheet-shaped cured product had been maintained in an oven setto 130° C. for 168 hours, the mass loss rate, the hardness and thethermal conductivity thereof were measured. The Mass loss rate was foundby using an expression: (Weight before the measurement−Weight after themeasurement)/Weight before the measurement×100=Mass loss rate (%). Thehardness and the thermal conductivity were measured in the same manneras the initial hardness and the initial thermal conductivity. Thesmaller the difference in hardness before the heat resistant test(initial hardness of the sheet) and after the heat resistant test, thelonger the flexibility is maintained.

[Durability]

The hardness difference (Δhardness) between the sheet initial hardnessand the sheet hardness after the heat-resistant test was determined. Asthis value becomes smaller, the flexibility of the sheet can bemaintained for a longer period; therefore, for example, when the sheetis interposed between a heat generating body and a heat conductive body,the contact area between these bodies is maintained for a long period oftime so that the thermal conductivity from the heat generating body tothe heat conductive body is not lowered to prepare a stable thermalconductive property for a long period of time.

No. 1-2

The same processes as those of No. 1-1 were carried out except that theliquid-state resin, which was composed of 30 parts of PEHA, 59 parts ofLMA serving as a monomer, 1 part of polyethylene glycol dimethacrylate(the aforementioned “Light Ester 9EG”) serving as a polyfunctionalmonomer and 10 parts of trimellitic acid ester-based liquid-stateplasticizer (the aforementioned “ADK-Cizer C880”), was used so that aplate-shaped cured product, a resin composition for a thermal conductivematerial and a sheet-shaped cured product thereof were obtained. Thesewere evaluated in the same manner as No. 1-1, and the results are shownin Table 2.

No. 1-3

The same processes as those of No. 1-1 were carried out except that theliquid-state resin, which was composed of 30 parts of PEHA, 64 parts ofLMA serving as a monomer, 1 part of polyethylene glycol dimethacrylate(the aforementioned “Light Ester 9EG”) serving as a polyfunctionalmonomer and 5 parts of trimellitic acid ester-based liquid-stateplasticizer (the aforementioned “ADK-Cizer C880”), was used so that aplate-shaped cured product, a resin composition for a thermal conductivematerial and a sheet-shaped cured product thereof were obtained. Thesewere evaluated in the same manner as No. 1-1, and the results are shownin Table 2.

No. 1-4

The same processes as those of No. 1-1 were carried out except that theliquid-state resin, which was composed of 30 parts of PEHA, 29 parts ofLMA serving as a monomer, 1 part of polyethylene glycol dimethacrylate(the aforementioned “Light Ester 9EG”) serving as a polyfunctionalmonomer and 40 parts of trimellitic acid ester-based liquid-stateplasticizer (the aforementioned “ADK-Cizer C880”), was used so that aplate-shaped cured product, a resin composition for a thermal conductivematerial and a sheet-shaped cured product thereof were obtained. Thesewere evaluated in the same manner as No. 1-1, and the results are shownin Table 2.

No. 1-5

The same processes as those of No. 1-1 were carried out except that theliquid-state resin, which was composed of 15 parts of PEHA, 34 parts ofLMA serving as a monomer, 1 part of polyethylene glycol dimethacrylate(the aforementioned “Light Ester 9EG”) serving as a polyfunctionalmonomer and 50 parts of trimellitic acid ester-based liquid-stateplasticizer (the aforementioned “ADK-Cizer C880”), was used so that aplate-shaped cured product, a resin composition for a thermal conductivematerial and a sheet-shaped cured product thereof were obtained. Thesewere evaluated in the same manner as No. 1-1, and the results are shownin Table 2.

No. 1-6

The same processes as those of No. 1-1 were carried out except that aliquid-state resin, which was composed of 40 parts of PEHA, 29 parts ofLMA serving as a monomer, 1 part of polyethylene glycol dimethacrylate(the aforementioned “Light Ester 9EG”) serving as a polyfunctionalmonomer and 30 parts of trimellitic acid ester-based liquid-stateplasticizer (the aforementioned “ADK-Cizer C880”), was used so that aplate-shaped cured product, a resin composition for a thermal conductivematerial and a sheet-shaped cured product thereof were obtained. Thesewere evaluated in the same manner as in No. 1-1, and the results areshown in Table 2.

No. 1-7

The same processes as those of No. 1-1 were carried out except that aliquid-state resin, which was composed of 30 parts of PEHA, 39 parts of2-ethylexyl acrylate, 1 part of polyethylene glycol dimethacrylate (theaforementioned “Light Ester 9EG”) serving as a polyfunctional monomerand 30 parts of trimellitic acid ester-based liquid-state plasticizer(the aforementioned “ADK-Cizer C880”), was used so that a plate-shapedcured product, a resin composition for a thermal conductive material anda sheet-shaped cured product thereof were obtained. These were evaluatedin the same manner as in No. 1-1, and the results are shown in Table 2.

No. 1-8

The same processes as those of No. 1-1 were carried out except that aliquid-state resin, which was composed of 30 parts of PEHA, 39 parts ofn-butyl acrylate, 1 part of polyethylene glycol dimethacrylate (theaforementioned “Light Ester 9EG”) serving as a polyfunctional monomerand 30 parts of trimellitic acid ester-based liquid-state plasticizer(the aforementioned “ADK-Cizer C880”), was used so that a plate-shapedcured product, a resin composition for a thermal conductive material anda sheet-shaped cured product thereof were obtained. These were evaluatedin the same manner as in No. 1-1, and the results are shown in Table 2.

No. 1-9

The same processes as those of No. 1-1 were carried out except that aliquid-state resin, which was composed of 30 parts of PEHA, 39 parts of2EHA serving as a monomer, 1 part of polyethylene glycol dimethacrylate(the above-mentioned “Light Ester 9EG”) serving as a polyfunctionalmonomer, 30 parts of trimellitic acid ester-based liquid-stateplasticizer (made by Asahi Denka Co., Ltd., tradename: “ADK-Cizer C79”),was used so that a plate-shaped cured product, a resin composition for athermal conductive material and a sheet-shaped cured product thereofwere obtained. These were evaluated in the same manner as in No. 1-1,and the results are shown in Table 2. Moreover, when 3 g of the appliedliquid-state plasticizer (made by Asahi Denka Co., Ltd., tradename:“ADK-Cizer C79”) was put on a watch glass having 5 cm in diameter, madeof aluminum, and held in an oven heated to 130° C. for 24 hours, themass loss rate thereof was 0.09%. Moreover, the viscosity thereof at 25°C. was 100 mPa·s and the solidifying point thereof was −22° C.

No. 1-10

The same processes as those of No. 1-1 were carried out except that aliquid-state resin, which was composed of 70 parts of the mixtureobtained in Synthesis Example 2, that is, 35 parts of PLMA and 35 partsof LMA serving as a monomer, as well as 1 part of polyethylene glycoldimethacrylate (the aforementioned “Light Ester 9EG”) serving as apolyfunctional monomer and 29 parts of trimellitic acid ester-basedliquid-state plasticizer (the aforementioned “ADK-Cizer C880”), was usedso that a plate-shaped cured product, a resin composition for a thermalconductive material and a sheet-shaped cured product thereof wereobtained. These were evaluated in the same manner as in No. 1-1, and theresults are shown in Table 2.

No. 1-11

The same processes as those of No. 1-1 were carried out except that aliquid-state resin, which was composed of 70 parts of the mixtureobtained in Synthesis Example 2, that is, 35 parts of PLMA and 35 partsof LMA serving as a monomer, as well as 1 part of polyethylene glycoldimethacrylate (the aforementioned “Light Ester 9EG”) serving as apolyfunctional monomer and 29 parts of trimellitic acid ester-basedliquid-state plasticizer (the aforementioned “ADK-Cizer C79”), was usedso that a plate-shaped cured product, a resin composition for a thermalconductive material and a sheet-shaped cured product thereof wereobtained. These were evaluated in the same manner as in No. 1-1, and theresults are shown in Table 2.

No. 1-12

The same processes as those of No. 1-1 were carried out except that aliquid-state resin, which was composed of 30 parts of PEHA, 39 parts of2EHA serving as a monomer, 1 part of polyethylene glycol dimethacrylate(the above-mentioned “Light Ester 9EG”) serving as a polyfunctionalmonomer, 30 parts of phosphoric acid ester-based liquid-stateplasticizer (made by Ajinomoto-Fine-Techno Co., Inc., tradename:“Kronitex TXP”), was used so that a plate-shaped cured product, a resincomposition for a thermal conductive material and a sheet-shaped curedproduct thereof were obtained. These were evaluated in the same manneras in No. 1-1, and the results are shown in Table 2. Moreover, when 3 gof the applied liquid-state plasticizer (made by Ajinomoto-Fine-TechnoCo., Inc., tradename: “Kronitex TXP) was put on a watch glass having 5cm in diameter, made of aluminum, and held in an oven heated to 130° C.for 24 hours, the mass loss rate thereof was 0.20%. Moreover, theviscosity thereof at 25° C. was 175 mPa·s and the solidifying pointthereof was −15° C.

No. 1-13 (for use in Comparison)

The same processes as those of No. 1-1 were carried out except that aliquid-state resin, which was composed of 69 parts of 2EHA serving as amonomer, 1 part of polyethylene glycol dimethacrylate (theaforementioned “Light Ester 9EG”) serving as a polyfunctional monomerand 30 parts of trimellitic acid ester-based liquid-state plasticizer(the aforementioned “ADK-Cizer C880”), was used (that is, no(meth)acrylic polymer that formed an essential component was contained)so that a plate-shaped cured product, a resin composition for a thermalconductive material and a sheet-shaped cured product thereof wereobtained. These were evaluated in the same manner as in No. 1-1, and theresults are shown in Table 2. The resulting sheet-shaped cured producthad a separation between the resin and the aluminum oxide serving as afiller, resulting in an uneven sheet. For this reason, the succeedingevaluations were not carried out.

No. 1-14 (for use in Comparison)

The same processes as those of No. 1-1 were carried out except that aliquid-state resin, which was composed of 99 parts of 2EHA serving as amonomer and 1 part of polyethylene glycol dimethacrylate (theaforementioned “Light Ester 9EG”) serving as a polyfunctional monomer,was used (that is, neither (meth)acrylic polymer nor liquid-stateplasticizer that formed essential components was contained) so that aplate-shaped cured product, a resin composition for a thermal conductivematerial and a sheet-shaped cured product thereof were obtained. Thesewere evaluated in the same manner as in No. 1-1, and the results areshown in Table 2. The resulting plate-shaped cured product had ahardness value of 78, which was greater than any of the plate-shapedcured products obtained in Examples in the present invention. Theresulting sheet had a separation between the resin and the aluminumoxide serving as a filler, resulting in an uneven sheet. For thisreason, the succeeding evaluations were not carried out.

No. 1-15 (for use in Comparison)

The same processes as those of No. 1-1 were carried out except that aliquid-state resin, which was composed of 30 parts of PEHA, 69 parts of2EHA serving as a monomer and 1 part of polyethylene glycoldimethacrylate (the aforementioned “Light Ester 9EG”) serving as apolyfunctional monomer, was used (that is, no liquid-state plasticizerthat formed an essential component was contained) so that a plate-shapedcured product, a resin composition for a thermal conductive material anda sheet-shaped cured product thereof were obtained. These were evaluatedin the same manner as in No. 1-1, and the results are shown in Table 2.The resulting plate-shaped cured product had a hardness value of 71 andthe resulting sheet had a hardness value of 80 in its initial hardness,and both of these values were greater than those of the cured productsobtained in Examples in the present invention. Consequently, in the casewhen the cured product is interposed between a heat-generating body,such as a PDP, an electric/electronic part, and a thermal conductivebody, such as a heat sink, a thermal conductive fin and a metal plate,so that the heat generated from the PDP, the electric/electronic partand the like is conducted, the contact area with these members tends tobecome smaller, resulting in degradation in the thermal conductivity.Moreover, the sheet hardness after the heat resistance test was 98, andthe hardness difference before and after the tests was greater than anyof those differences obtained in Examples of the present invention. Forthis reason, it is clear that this sheet fails to provide a long-termflexibility, resulting in a failure to provide a stable thermalconductive property.

Here, the meanings of abbreviations used in Table 2 are explained asfollows:

PEHA: Poly-2-ethylhexyl acrylate obtained in Synthesis Example 1

PLMA: Polylauryl methacrylate obtained in Synthesis Example 2

2EHA: 2-ethylhexyl acrylate

LMA: Lauryl methacrylate

BA: n-Butyl acrylate

9EG: Polyethylene glycol dimethacrylate made by Kyoei Chemical Co.,tradename: “Light Ester 9EG”

C880: Liquid-state plasticizer made by Asahi Denka Co., Ltd., tradename:“ADK-Cizer C880”

C79: Liquid-state plasticizer made by Asahi Denka Co., Ltd., tradename:“ADK-Cizer C79”

TMPO70: Polymerization initiator made by Kayaku Akzo Corporation,tradename: “Kayaester TMPO-70”

A-515: Antifoamer made by BYK-Chemie Japan KK, tradename: “A-515”

Δhardness: Hardness difference between a sheet initial hardness valueand the sheet hardness value after the heat-resistant test TABLE 2(Experiment 1) No. 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-9 1-10 1-11 1-121-13 1-14 1-15 Components Components PEHA 30 30 30 30 15 40 30 30 30 0 030 0 0 30 of resin of liquid- PLMA 0 0 0 0 0 0 0 0 0 35 35 0 0 0 0composition state resin 2EHA 0 0 0 0 0 0 39 0 39 0 0 0 69 99 69 LMA 3959 64 29 34 29 0 0 0 35 35 39 0 0 0 BA 0 0 0 0 0 0 0 39 0 0 0 0 0 0 09EG 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 C880 30 10 5 40 50 30 30 30 0 29 0 2930 0 0 C79 0 0 0 0 0 0 0 0 30 0 29 0 0 0 0 Kronitex 0 0 0 0 0 0 0 0 0 00 30 0 0 0 TXP TMPO70 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 A-515 0.1 0.1 0.10.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Aluminum 400 400 400 400400 400 400 400 400 400 400 400 400 400 400 oxide (AS-10) Plate-shapedhardness (F type) 12 40 58 7 5 14 13 13 12 11 10 15 18 78 71 Sheetmoldability ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ x x ∘ Sheet initial hardness(C-type) 40 55 60 31 23 43 45 50 41 40 42 39 — — 80 Sheet initialthermal conductivity 1.5 1.6 1.4 1.5 1.5 1.4 1.6 1.6 1.6 1.6 1.5 1.5 — —1.4 (W/m · K) Heat resistance Mass loss 0.3 0.4 0.4 0.4 0.3 0.3 0.3 0.40.6 0.4 0.6 0.9 — — 0.3 rate (%) Sheet 43 58 65 33 24 46 49 53 47 43 4848 — — 98 hardness (C-type) Thermal 1.5 1.6 1.5 1.5 1.5 1.4 1.6 1.7 1.71.7 1.6 1.7 — — 1.5 conductivity (W/m · K) Durability (Δ hardness) 3 3 52 1 3 4 3 6 3 6 9 — — 18No. 1-16

A liquid-state resin, composed of the mixture obtained in SynthesisExample 2 (70 parts), that is, 35 parts of PLMA and 35 parts of LMAserving as a monomer, as well as 1 part of polyethylene glycoldimethacrylate (the aforementioned “Light Ester 9EG”) serving as apolyfunctional monomer, 30 parts of phthalic acid ester-basedliquid-state plasticizer (made by Kao Corporation, tradename: “Vinycizer124”), 2 parts of t-amylperoxy 3,5,5-trimethyl hexanoate serving as athermal polymerization initiator with a 10-hour half-life periodtemperature of 95° C. (made by Kayaku Akzo Corporation: tradename:“Kayaester AN”), and 1300 parts of aluminum oxide having a thermalconductivity of 30 W/m·K (made by Showa Denko K.K.: item number AS-40)were kneaded by using a pressurized kneader. Moreover, when 3 g of theapplied liquid-state plasticizer (the above-mentioned “Vinycizer-124”)was put on a watch glass having 5 cm in diameter, made of aluminum, andheld in an oven heated to 130° C. for 24 hours, the mass loss ratethereof was 0.43%. Moreover, the viscosity thereof at 25° C. was 65mPa·s and the solidifying point thereof was −22° C.

Thereafter, the resulting kneaded matter was extruded into a gap betweentwo PET films by using an extruder with a thickness set to 1 mm so thata sheet-shaped product was obtained. The resulting sheet was uniform,and free from a separation between the resin and the inorganic filler.Moreover, neither bubbles nor irregularities were observed on thesurface. Consequently, it had a superior pre-forming property.

Next, spacers, which were made of silicon and had a thickness of 1 mm,were attached onto the periphery of the resulting sheet-shaped product,and the sheet was put on a flat-plate mold heated to 120° C., andsubjected to a press-molding process for 20 minutes under a pressure of10 kg/cm². The resulting sheet-shaped cured product had neitherirregularities nor defects on its surface. Consequently, it had superiormoldability.

The thermal conductivity of this sheet-shaped cured product was 3.3W/m·K, thereby making it possible to exert a superior heat-releasingproperty. When its flexibility (hardness) was measured, a value of 49was obtained. The hardness was measured by using an Asker rubber A-typehardness tester made by Koubunshi Keiki Co., Ltd. at 25° C. inaccordance with a durometer hardness test (type-A test) under JIS K6253.

Experiment 2 (Experiments Relating to a Resin Composition in which a(meth)acrylic Polymer (I-a) is Synthesized in a Liquid-statePlasticizer) Production Examples 1 to 5

Into a glass container equipped with a stirring device, a gasintroducing pipe, a thermometer, a reflux condenser and a droppingfunnel were charged a first (meth)acrylic polymerizable monomer [and asecond (meth)acrylic polymerizable monomer, if necessary], a firstliquid-state plasticizer and a chain transfer agent, and the inner gasof the container was replaced with a nitrogen gas so that the oxygenconcentration of the gaseous phase portion inside the reaction containerwas set to 0.1 mass % (charging stage). This was heated to apredetermined temperature (A), and a polymerization initiator, dilutedwith a diluting liquid-state plasticizer, if necessary, was droppedthrough the dropping funnel over a predetermined period of time(reaction starting stage). Next, the resulting mixture was continuouslystirred at a predetermined temperature (B) for a predetermined period oftime (reaction continuing stage). Thereto was further added apolymerization initiator, if necessary, and the stirring process wascontinuously carried out at a predetermined temperature (C) for apredetermined period of time (reaction maturing stage). Air was blowninto this to be cooled, and the polymerization process was completed sothat mixtures 2-A to 2-E containing polymers 2-A to 2E, etc. wereobtained. Here, in any of Examples, there was no uncontrollable progressin the polymerization reaction. Those processes are shown in thefollowing Table 3, in detail. In Production Example 5, a polyetherester-based liquid-state plasticizer (made by Asahi Denka Co., Ltd.,tradename: “ADK-Cizer RS700”) was used; however, this liquid-stateplasticizer had a big mass loss rate (2.95%), and failed to satisfy thescope of the present invention. TABLE 3 (Experiment 2) ProductionProduction Production Example 1 Example 2 Example 3 Charging stage First(meth)acrylic Lauryl methacrylate 2-ethylhexyl acrylate 2-ethylhexylacrylate monomer 70 parts by mass 40 parts by mass 70 parts by massFirst liquid-state Trimellitic acid ester Trimellitic acid esterTrimellitic acid ester plasticizer 30 parts by mass*¹ 55 parts by mass*¹30 parts by mass*¹ Chain transfer agent α-methyl styrene dimer α-methylstyrene dimer α-methyl styrene dimer 0.3 part by mass 0.1 part by mass0.5 part by mass Gaseous-phase portion   0.1%  0.0%   0.0% oxygenconcentration*² Reaction Polymerization initiator AzoisobutyronitrileDimethyl 2,2-azobis Azoisobutyronitrile starting stage 0.08 part by mass(2-methyl propionate) 0.05 part by mass 0.1 part by mass Dilutingliquid-state — Trimellitic acid ester 5 — plasticizer parts by weightTemperature (A)/ 80° C./quickly 75° C./2 hours 80° C./quickly droppingtime Reaction Temperature (B)/ Until the viscosity at   75° C./1.5 hoursUntil the viscosity at continuous stage continuous time 80° C./25° C.has 80° C./25° C. has reached 2000 mPa · s reached 2000 mPa · s ReactionPolymerization initiator — Dimethyl 2,2-azobis — maturing stage(2-methyl propionate) 0.02 part by mass Temperature (C)/ — 90° C./2hours — maturing time Polymerization rate 57% 99.9% 57% Reaction NameMixture 2-A Mixture 2-B Mixture 2-C mixture Compo- (Meth)acrylic monomer30% by mass 0.04% by mass   30% by mass sition (Meth)acrylic polymer 40%by mass 40% by mass 40% by mass Liquid-state plasticizer 30% by mass 60%by mass 30% by mass Vis- Rotor No./number of No. 2/12 rpm No. 3/12 rpmNo. 2/12 rpm cosity revolutions Measured value (25° C.) 2250 mPa · s8500 mPa · s 1800 mPa · s Polymer Name Polymer 2-A Polymer 2-B Polymer2-C properties Weight average 156000 506000 145000 molecular weight MwNumber average  61000 101000  59000 molecular weight Mn Glass transition−65° C. −60° C. −63° C. temperature Tg Production Example 4 ProductionExample 5 Charging stage First (meth)acrylic monomer 2-ethylhexylacrylate 2-ethylhexyl acrylate 60 parts by mass 40 parts by mass Firstliquid-state plasticizer Trimellitic acid ester Polyether ester 55 40parts by mass*¹ parts by mass*⁴ Chain transfer agent α-methyl styrenedimer α-methyl styrene dimer 0.4 part by mass 0.3 part by massGaseous-phase portion oxygen   0.0%  0.1% concentration*² ReactionPolymerization initiator Azoisobutyronitrile Dimethyl 2,2-azobisstarting stage 0.05 part by mass (2-methyl propionate) 0.1 part by massDiluting liquid-state plasticizer — Polyether ester 5 parts by mass*⁴Temperature (A)/dropping time 80° C./quickly 75° C./2 hours ReactionTemperature (B)/continuous Until the viscosity at   75° C./1.5 hourscontinuous stage time 80° C./25° C. has reached 2000 mPa · s ReactionPolymerization initiator — Dimethyl 2,2-azobis maturing stage (2-methylpropionate) 0.02 part by mass Temperature (C)/maturing time — 90° C./2hours Polymerization rate 50% 99.9% Reaction Name Mixture 2-D Mixture2-E mixture Composition (Meth)acrylic monomer 30% by mass 0.04% bymass   (Meth)acrylic polymer 30% by mass 40% by mass Liquid-stateplasticizer 40% by mass 60% by mass Viscosity Rotor No./number of No.2/12 rpm No. 3/12 rpm revolutions Measured value (25° C.) 2050 mPa · s6500 mPa · s Polymer Name Polymer 2-D Polymer 2-E properties Weightaverage molecular 185000 406000 weight Mw Number average molecular 79000  81000 weight Mn Glass transition temperature −63° C. −60° C. Tg*¹made by Asahi Denka Co., Ltd., tradename: “ADK-Cizer C880”, viscosity:100 mPa · s (25° C.), mass loss rate after having been maintained at130° C. for 24 hours: 0.07% by mass, solidifying point: −21° C.*²measured by an oxygen densitometer (Model No. UC-12) made by CentralScience Co., Ltd.*³set so that a hydroxyl-group-containing monomer accounts for 3 mol %in the entire polymerizable monomer*⁴made by Asahi Denka Co., Ltd., tradename: “ADK-Cizer RS700”,viscosity: 30 mPa · s (25° C.), mass loss rate after having beenmaintained at 130° C. for 24 hours: 2.95% by mass, solidifying point:−53° C.

In Table 3, the polymerization rate was found by calculating the amountof the residual first (meth)acrylic polymerizable monomer using gaschromatography (GC).

Preparation Examples 1 to 5

The above-mentioned mixtures 2-A to 2-E were mixed with various othersubstances at ratios shown in the following Table 4 so that(meth)acrylic liquid-state resin compositions 2-A to 2-E havingcompositions shown in the following Table 4 were prepared.

Those resins that virtually contain a (meth)acrylic polymerizablemonomer are cured through radical polymerization (thermalpolymerization), and consequently, referred to as “polymerizable resin”.TABLE 4 (Experiment 2) Preparation Preparation Preparation PreparationPreparation Example 1 Example 2 Example 3 Example 4 Example 5Methacrylic Acrylic Acrylic Acrylic Acrylic polymerizable polymerizablepolymerizable polymerizable polymerizable liquid-state resinliquid-state resin liquid-state resin liquid-state resin liquid-stateresin Name composition 2-A composition 2-B composition 2-C composition2-D composition 2-E Mixture Mixture Mixture 2-A Mixture 2-B Mixture 2-CMixture 2-D Mixture 2-E ratio 99.5 parts by 60 parts by mass 99.5 partsby 70 parts by mass 60 parts by mass mass mass Additional — 2-ethylhexyl— 2-ethylhexyl 2-ethylhexyl (meth)acrylic acrylate 49.5 acrylate 29.5acrylate 49.5 monomer parts by mass parts by mass parts by massPolyfunctional Polyethylene Polyethylene Polyethylene PolyethylenePolyethylene monomer glycol glycol glycol glycol glycol dimethacrylate*¹ dimethacrylate *¹ dimethacrylate *¹ dimethacrylate *¹ dimethacrylate*¹ 0.5 part by mass 0.5 part by mass 0.5 part by mass 0.5 part by mass0.5 part by mass Polymerization — Hydroquinone — — Hydroquinoneinhibitor 0.05 part by mass 0.05 part by mass Composition A:(Meth)acrylic 30% by mass 45% by mass 30% by mass 50% by mass 45% bymass monomer B: (Meth)acrylic 40% by mass 22% by mass 40% by mass 21% bymass 22% by mass polymer C: Liquid-state 30% by mass 33% by mass 30% bymass 28% by mass 33% by mass plasticizer D: Polyfunctional 0.5% by mass 0.5% by mass  0.5% by mass  0.5% by mass  0.5% by mass  monomer A/B 75/100 207/100  75/100 241/100 207/100 D/(A + B) 0.7/100  0.7/1000.7/100  0.7/100  0.7/100 Viscosity Rotor No./number No. 2/12 rpm No.1/12 rpm No. 2/12 rpm No. 1/12 rpm No. 1/12 rpm of revolutions Measuredvalue 2150 mPa · s 250 mPa · s 1800 mPa · s 310 mPa · s 180 mPa · s (25°C.)*¹ made by Kyoei Chemical Co., tradename: “Light Ester 9EG”No. 2-1

Polymerizable liquid-state methacrylic resin composition 2-A(100 partsby mass), t-amyl peroxy-2-ethylhexanoate (made by Kayaku AkzoCorporation: tradename: “Trigonox 121-50E”) (1 part by mass) serving asa radical polymerization initiator, an antifoamer (the aforementioned“A-515”) (0.1 part by mass), aluminum oxide (the aforementioned AS-10;thermal conductivity 30 W/m·K) (400 parts by mass) were uniformlykneaded, and then defoamed. The above-mentioned defoamed matter waspoured into a glass cell on the bottom of which a PET film that had beensubjected to a releasing treatment was affixed so as to have a thicknessof 1 mm, and this was heated in an oven at 100° C. for one hour, andthen at 120° C. for one hour to be polymerized (cured).

Nos. 2-1 to 2-5

The same processes as those of No. 2-1 were carried out except that inplace of the polymerizable liquid-state methacrylic resin composition2-A, polymerizable liquid-state acrylic resin compositions 2-B to 2-Ewere used.

The resulting sheet-shape cured products obtained in Nos. 2-1 to 2-5were evaluated in the same manner as in the aforementioned Experiment 1.Here, with respect to the heat resistant decomposing property, theheating process of the sheet-shaped cured product at 130° C. wasprolonged to 336 hours as well as to 504 hours so that the hardness wasexamined in the same manner as described earlier. TABLE 5 (Experiment 2)No. 2-1 2-2 2-3 2-4 2-5 Liquid-state resin composition MethacrylicMethacrylic Methacrylic Methacrylic Methacrylic to be used polymerizablepolymerizable polymerizable polymerizable polymerizable liquid-stateresin liquid-state resin liquid-state resin liquid-state resinliquid-state resin composition 2-A composition 2-B composition 2-Ccomposition 2 D composition 2-E Sheet initial hardness (C type) 23 21 2321 21 Sheet initial thermal 1.5 W/m · k 1.6 W/m · k 1.6 W/m · k 1.6 W/m· k 1.5 W/m · k conductivity (W/m · K) Heat Mass loss rate (%) 0.4% 0.3%0.2% 0.2% 3.8% resistance Sheet hardness 26 24 24 23 41 (C type) Thermalconductivity 1.6 W/m · k 1.6 W/m · k 1.6 W/m · k 1.6 W/m · k 1.6 W/m · k(W/m · K) Durability (Δ hardness) +3 +3 +1 +2 +20  Heat resistantdecomposing 27 25 25 24 70 property: 336 hrs later Heat resistantdecomposing 30 27 27 24 >100  property: 504 hrs later

Each of polymerizable liquid-state resin compositions 2-A to 2-D makesit possible to reduce the amount of use of the liquid-state plasticizer,with the viscosity being maintained in a low level (see Table 4).Moreover, in comparison with liquid-state methacrylic resin composition2-A, liquid-state acrylic resin compositions 2-B to 2-D further achievea low-level viscosity (see Table 4). Here, liquid-state resincompositions 2-A to 2-D can be produced without using virtually anyspecial catalyst and solvent. It is in particular notable thatliquid-state acrylic resin compositions 2-B to 2-D can be producedwithout virtually using any special catalyst and solvent.

Moreover, the cured products obtained from polymerizable liquid-stateresin compositions 2-A to 2-D were free from bleeding even after havingbeen heated for a very long period of time at high temperature, and hada superior heat-resistant decomposing property (see FIG. 5). In the caseof No. 2-5 in which a polyether ester-based material that was inferiorin heat resistance was used as the liquid-state plasticizer, the massloss rate after the heating process was high, indicating degradation inthe heat resistant property (see FIG. 5).

Experiment 3 (Experiments Relating to a Resin Composition in whichPolymer (I) is a Crosslinking Polymer (I-b)) Synthesis Example 3

Into a container equipped with a thermometer, a stirring device, a gasintroducing pipe, a reflux condenser and a dropping funnel were charged39.48 parts of 2EHA, 0.52 part of 2-hydroxyethyl acrylate (HEA) (with ahydroxyl-group-containing monomer being set to 2 mol % in the entirepolymerizable monomers), 50 parts of trimellitic acid ester-basedliquid-state plasticizer (the aforementioned “ADK-Cizer C880”) servingas a liquid-state plasticizer, and the inner gas of the container wasreplaced with a nitrogen gas. This was heated to 75° C., and a mixtureof 0.05 part of dimethyl 2,2-azobis (2-methyl propionate) serving as apolymerization initiator and 10 parts of a trimellitic acid ester-basedliquid-state plasticizer (the aforementioned “ADK-Cizer C880”) wascharged into the dropping funnel, and dropped into the container inthree hours. Thereto was further added 0.02 part of dimethyl 2,2-azobis(2-methyl propionate) serving as a polymerization initiator, and theresulting mixture was heated to 90° C. and allowed to undergo apolymerization reaction for 3 hours. Prior to the completion of thepolymerization reaction, 0.4 part of dibutyltin dilaurate serving ascrosslinking accelerator was added thereto and air was further blownthereto to cool the system so that the polymerization was completed;thus, a mixture of an acrylic copolymer containing 2-mol % hydroxylgroup serving as a crosslinking polymer and a trimellitic acidester-based liquid-state plasticizer (hereinafter, referred to asacrylic resin 3-A) was obtained. The residual 2EHA, confirmed by gaschromatography (GC), was 0.1%, and the acrylic copolymer containing2-mol % hydroxyl group, serving as a crosslinking polymer in the acrylicresin 3-A, was 39.9%.

The viscosity of the resulting acrylic resin 3-A at 25° C. was 12980mPa·s. With respect to the molecular weight of the polymer measured byGPC, the weight-average molecular weight Mw was 1106000 and thenumber-average molecular weight Mn was 101000. Moreover, the glasstransition point temperature of the acrylic copolymer containing 2-mol %hydroxyl-group serving as a crosslinking polymer, measured by adifferential scanning calorimeter according to a conventional method,was −64° C.

Synthesis Example 4

The same processes as those of Synthesis Example 3 were carried outexcept that the charged materials into the reaction container werechanged to 39.70 parts of 2EHA, 0.30 part of HEA (with ahydroxyl-group-containing monomer being set to 1 mol % in the entirepolymerizable monomers) and 50 parts of trimellitic acid ester-basedliquid-state plasticizer (the aforementioned “ADK-Cizer C880”) servingas a liquid-state plasticizer so that a mixture of an acrylic copolymercontaining 1-mol % hydroxyl group serving as a crosslinking polymer anda trimellitic acid ester-based liquid-state plasticizer (hereinafter,referred to as acrylic resin 3-B) was obtained.

The residual 2EHA, confirmed by gas chromatography (GC), was 0.1%, andthe acrylic copolymer containing 1-mol % hydroxyl group, serving as acrosslinking polymer in the acrylic resin 3-B, was 39.9%. The viscosityof the resulting acrylic resin 3-B at 25° C. was 11500 mPa·s. Withrespect to the molecular weight of the polymer measured by GPC, theweight-average molecular weight Mw was 1006000 and the number-averagemolecular weight Mn was 105000. Moreover, the glass transition pointtemperature of the acrylic copolymer containing 1-mol % hydroxyl group,measured by a differential scanning calorimeter according to aconventional method, was −62° C.

Synthesis Example 5

The same processes as those of Synthesis Example 3 were carried outexcept that the trimellitic acid ester-based liquid-state plasticizerwas changed to the aforementioned “ADK-Cizer C79” so that a mixture ofan acrylic copolymer containing 2-mol % hydroxyl group serving as acrosslinking polymer and a trimellitic acid ester-based liquid-stateplasticizer (hereinafter, referred to as acrylic resin 3-C) wasobtained. The residual 2EHA, confirmed by gas chromatography (GC), was0.1%, and the acrylic copolymer containing 2-mol % hydroxyl group,serving as a crosslinking polymer in the acrylic resin 3-C, was 39.9%.The viscosity of the resulting acrylic resin 3-C at 25° C. was 11500mPa·s. With respect to the molecular weight of the polymer measured byGPC, the weight-average molecular weight Mw was 1106000 and thenumber-average molecular weight Mn was 135000. Moreover, the glasstransition point temperature of the acrylic copolymer containing 2-mol %hydroxyl group, measured by a differential scanning calorimeteraccording to a conventional method, was −65° C.

No. 3-1

To 100 parts of a liquid-state resin composed of 62 parts of the acrylicresin 3-A and 38 parts of the trimellitic acid-based liquid-stateplasticizer (the aforementioned “ADK-Cizer C880” (a liquid-state resincontaining about 25% of a 2-mol % hydroxyl-group-containing acryl-basedcopolymer serving as a crosslinking polymer and 75% of a liquid-stateplasticizer) were added 0.1 part of an antifoamer (the aforementioned“A-515”) and 0.86 part of isophorone diisocyanate (in which the amountof isocyanate was mole equivalent to the amount of hydroxyl groups ofthe acrylic copolymer in the liquid-state resin) serving as acrosslinking agent, and the resulting mixture was defoamed, and pouredinto a glass cell having a PET film that was set to a thickness of 15 mmand had been subjected to a releasing treatment, and this was heated inan oven at 80° C. for 2 hours so that the liquid-state resin was gelledto prepare a plate-shaped cured product.

Next, 100 parts of the liquid-state resin, 0.1 part of the antifoamer(the aforementioned “A-515”), 0.86 part of isophorone diisocyanateserving as a crosslinking agent, 200 parts of aluminum oxide having athermal conductivity of 30 W/m·K (the aforementioned AS-10) wereuniformly kneaded to prepare a resin composition for a thermalconductive material. Thereafter, the resin composition for a thermalconductive material was subjected to a defoaming process, and pouredinto a glass cell having a PET film with a thickness of 1 mm, which hadbeen subjected to a releasing treatment, and heated at 80° C. for twohours so that the reaction between the hydroxyl group and the isocyanategroup in the composition was completed to prepare a sheet-shaped curedproduct of the resin composition for a thermal conductive material. Withrespect to the plate-shaped cured product and the sheet-shaped curedproduct, the properties thereof were evaluated in the same manner as inExperiment 1, and the results are shown in Table 6. Here, the evaluationon the heat resistance was carried out at 100° C. for 168 hours.

No. 3-2

The same processes as those of No. 3-1 were carried out except that 100parts of a liquid-state resin containing 75 parts of the acrylic resin3-A and 25 parts of the trimellitic acid-based liquid-state plasticizer(the aforementioned “ADK-Cizer C880”) (a liquid-state resin containingabout 30% of a 2-mol % hydroxyl-group-containing acryl-based copolymerserving as a crosslinking polymer and 70% of a liquid-stateplasticizer), with 1.03 parts of isophorone diisocyanate (in which theamount of isocyanate was mole equivalent to the amount of hydroxylgroups of the acrylic copolymer in the liquid-state resin) serving as acrosslinking agent being added thereto, were used so that a plate-shapedcured product of the liquid-state resin and a sheet-shaped cured productof the resin composition for a thermal conductive material wereobtained. These were evaluated in the same manner as in No. 3-1, and theresults are shown in Table 6.

No. 3-3

The same processes as those of No. 3-1 were carried out except that 100parts of a liquid-state resin containing 62 parts of the acrylic resin3-B and 38 parts of the trimellitic acid-based liquid-state plasticizer(the aforementioned “ADK-Cizer C880”) (a liquid-state resin containingabout 25% of a 1-mol % hydroxyl-group -containing acryl-based copolymerserving as a crosslinking polymer and about 75% of a liquid-stateplasticizer), with 0.43 part of isophorone diisocyanate serving as acrosslinking agent being added thereto, were used so that a plate-shapedcured product of the liquid-state resin and a sheet-shaped cured productof the resin composition for a thermal conductive material wereobtained. These were evaluated in the same manner as in No. 3-1, and theresults are shown in Table 6.

No. 3-4

The same processes as those of No. 3-1 were carried out except that 100parts of a liquid-state resin containing 75 parts of the acrylic resin3-B and 25 parts of the trimellitic acid-based liquid-state plasticizer(the aforementioned “ADK-Cizer C880”) (a liquid-state resin containingabout 30% of a 1-mol % hydroxyl-group-containing acryl-based copolymerserving as a crosslinking polymer and about 70% of a liquid-stateplasticizer), with 0.52 part of isophorone diisocyanate serving as acrosslinking agent being added thereto, were used so that a plate-shapedcured product of the liquid-state resin and a sheet-shaped cured productof the resin composition for a thermal conductive material wereobtained. These were evaluated in the same manner as in No. 3-1, and theresults are shown in Table 6.

No. 3-5

The same processes as those of No. 3-1 were carried out except that 100parts of a liquid-state resin containing 62 parts of the acrylic resin3-C and 38 parts of the trimellitic acid-based liquid-state plasticizer(the aforementioned “ADK-Cizer C79”) (a liquid-state resin containingabout 25% of a 2-mol % hydroxyl- group-containing acryl-based copolymerserving as a crosslinking polymer and about 75% of a liquid-stateplasticizer) was used so that a plate-shaped cured product of theliquid-state resin and a sheet-shaped cured product of the resincomposition for a thermal conductive material were obtained. These wereevaluated in the same manner as in No. 3-1, and the results are shown inTable 6.

No. 3-6

The same processes as those of No. 3-1 were carried out except that 100parts of a liquid-state resin containing 75 parts of the acrylic resin3-C and 25 parts of the trimellitic acid-based liquid-state plasticizer(the aforementioned “ADK-Cizer C79”) (a liquid-state resin containingabout 30% of a 2-mol % hydroxyl-group-containing acryl-based copolymerserving as a crosslinking polymer and about 70% of a liquid-stateplasticizer) was used so that a plate-shaped cured product of theliquid-state resin and a sheet-shaped cured product of the resincomposition for a thermal conductive material were obtained. These wereevaluated in the same manner as in No. 3-1, and the results are shown inTable 6.

No. 3-7

The same processes as those of No. 3-1 were carried out except that thealuminum oxide was changed to 100 parts of boron nitride having athermal conductivity of 50 W/m·K (made by KCM Corporation; Item No.BN-100) so that a plate-shaped cured product of the liquid-state resinand a sheet-shaped cured product of the resin composition for a thermalconductive material were obtained. These were evaluated in the samemanner as in No. 3-1, and the results are shown in Table 6.

No. 3-8

The same processes as those of No. 3-1 were carried out except that thealuminum oxide was changed to 200 parts of aluminum nitride having athermal conductivity of 120 W/m·K (made by Toyo Aluminum K.K.; Item No.R-15) so that a plate-shaped cured product of the liquid-state resin anda sheet-shaped cured product of the resin composition for a thermalconductive material were obtained. These were evaluated in the samemanner as in No. 3-1, and the results are shown in Table 6.

No. 3-9 (for Use in Comparison)

Into a container equipped with a thermometer, a stirring device, a gasintroducing pipe, a reflux condenser and a dropping funnel were charged39.70 parts of 2EHA, 0.30 part of HEA (with a hydroxyl-group-containingmonomer being set to 1 mol % in the entire monomers), 50 parts oftoluene and 0.2 part of α-methyl styrene serving as a chain transferagent, and the inner gas of the container was replaced with a nitrogengas. This was heated to 80° C., and a mixture of 0.05 part ofazoisobutyronitrile serving as a polymerization initiator and 10 partsof toluene was charged into the dropping funnel, and dropped into thecontainer in two hours. To this was further added 0.01 part ofazoisobutyronitrile, and the resulting mixture was heated to 90° C. andallowed to undergo a polymerization reaction for 3 hours. Prior to thecompletion of the polymerization reaction, 0.4 part of dibutyltindilaurate serving as a crosslinking accelerator was added thereto andair was further blown thereto to cool the system so that thepolymerization was completed; thus, a toluene solution of the resin,containing 40% of 1-mol % hydroxyl-group-containing copolymer serving asa crosslinking polymer, was obtained. With respect to the molecularweight of the copolymer measured by GPC, the weight-average molecularweight Mw was 306000 and the number-average molecular weight Mn was101000. Moreover, the glass transition point temperature of the polymer,measured by a differential scanning calorimeter according to aconventional method, was −60° C.

Next, a mixture, prepared by adding 0.69 part of isophorone diisocyanate(in which the amount of isocyanate was mole equivalent to the amount ofhydroxyl groups of the crosslinking polymer in the liquid-state resin)serving as a crosslinking agent to 100 parts of the toluene solution ofthe resin containing no liquid-state plasticizer as an essentialcomponent of its liquid-state resin component, was developed on a PETfilm that was set to a thickness of 15 mm and had been subjected to areleasing treatment, and the toluene was completely distilled off underreduced pressure of the system. Next, this was heated in an oven at 80°C. for two hours so that the hydroxyl group and isocyanate were allowedto react in the polymer to obtain a gelled matter. The resulting gelledmatter was evaluated in the same manner as in No. 3-1, and the resultsare shown in Table 6.

Next, to 100 parts of the toluene solution of the resin were added 0.69part of isophorone diisocyanate serving as a crosslinking agent and 80parts of aluminum oxide (the aforementioned AS-10) (the amount ofaddition of which was 200 parts based on 100 parts of the crosslinkingpolymer in the toluene solution of the resin), and this was uniformlykneaded to prepare a resin composition for a thermal conductivematerial. Thereafter, the resin composition for a thermal conductivematerial was developed on a PET film that had been subjected to areleasing treatment so as to form a thickness of 1 mm, and the toluenewas completely distilled off under reduced pressure in the system. Next,this was heated in an oven at 80° C. for two hours so that the hydroxylgroup and isocyanate were allowed to react in the polymer to obtain acured product of a sheet-shaped resin composition for a thermalconductive material. The resulting sheet was evaluated in the samemanner as in No. 3-1. The results of the evaluation are shown in Table6.

The value of hardness of the gel obtained in No. 3-9 for use incomparison was 95. This is presumably because the gel was not obtainedby holding the liquid-state plasticizer in the crosslinking polymer withthe result that the hardness of the gel became high to causedeterioration in flexibility. Moreover, the initial hardness of thesheet was 70, which was greater than any of the cured products obtainedin Examples of the present invention. Consequently, in the case when thecured product is interposed between a heat-generating body, such as aPDP, an electric part and an electronic part, and a thermal conductivebody, such as a heat sink, a thermal conductive fin and a metal plate,so that the heat generated from the PDP, the electric part or theelectronic part is heat-released, the contact area with these memberstends to become smaller, resulting in degradation in the heat-releasingproperty. Moreover, the sheet hardness after the heat resistance testwas 89 with a mass loss rate of 0.6%, and the amount of change in thehardness before and after the tests was greater than any of thoseobtained in Examples of the present invention. For this reason, it isclear that this sheet fails to provide a long-term flexibility,resulting in a failure to provide a stable heat-releasing property.

No. 3-10 (for Use in Comparison)

Toluene was completely distilled off from the toluene solution of theresin obtained in No. 3-9 to prepare a 1-mol % hydroxyl-group-containingcopolymer serving as a crosslinking polymer.

To 100 parts of a thermo-softening resin containing 75 parts of the1-mol % hydroxyl-group-containing copolymer serving as a crosslinkingpolymer and 25 parts of paraffin (made by Nippon Seiro Co., Ltd.; ItemNo. Paraffin Wax 115) serving as a thermosoftener that was in a solidstate at normal temperature with a melting point of 47° C. (that is, noliquid-state plasticizer that was essential for the liquid-state resinwas contained) was added 1.30 parts of isophorone diisocyanate (whichwas mole equivalent to the amount of hydroxyl groups of the crosslinkingpolymer in the thermosoftening resin) serving as a crosslinking agent toprepare a mixture, and this was developed on a PET film that had beensubjected to a releasing treatment to be set to a thickness of 15 mm,and heated in an oven at 80° C. for two hours so that the hydroxyl groupand isocyanate were allowed to react in the polymer to obtain a gelledmatter. The resulting gelled matter was evaluated in the same manner asin No. 3-1, and the results are shown in Table 6.

Next, 100 parts of the thermosoftening resin, 1.30 parts of isophoronediisocyanate serving as a crosslinking agent and 200 parts of aluminumoxide having a thermal conductivity of 30 W/m·K (the aforementionedAS-10) were kneaded at 50° C. for 30 minutes by using a pressurizedkneader. Thereafter, this was extruded into a gap between 2 sheets ofPET films to be set to a thickness of 1 mm by using an extruder so thata sheet-shaped resin composition for a thermal conductive material wasprepared. The resulting sheet-shaped resin composition for a thermalconductive material was heated at 80° C. for 2 hours so that thereaction between the hydroxyl group and isocyanate group in thecomposition was completed. The resulting sheet was evaluated in the samemanner as in No. 3-1, and the results are shown in Table 6.

The value of hardness of the resulting gel was 90. This is presumablybecause the gel was not obtained by holding the liquid-state plasticizerin the crosslinking polymer with the result that the hardness of the gelbecame high to cause deterioration in flexibility. Moreover, the initialhardness of the sheet was 60, which was greater than any of the curedproducts obtained in Examples of the present invention. Consequently, inthe case when the cured product is interposed between a heat-generatingbody, such as a PDP, an electric part and an electronic part, and athermal conductive body, such as a heat sink, a thermal conductive finand a metal plate, so that the heat generated from the PDP, the electricpart or the electronic part is heat-released, the contact area withthese members tends to become smaller, resulting in degradation in theheat-releasing property.

Here, the resulting sheet was uniform without a separation between theresin and the applied inorganic filler; however, there wereirregularities and bubbles on the surface, and was inferior in thesurface smoothness. In other words, the sheet was inferior in themoldability.

Moreover, as a result of heat resistant tests, the mass loss rate was6.1%, with the sheet hardness exceeding the maximum value 100. This ispresumably because the mass loss rate became greater due to evaporationof the thermosoftening agent applied thereto to cause a change inhardness. Consequently, the resulting sheet failed to have flexibilityfor a long period of time, resulting in degradation in stableheat-releasing property. Moreover, a number of swellings occurred on thesheet after the heat resistant test.

Here, the meanings of abbreviations used in Table 6 are explained asfollows:

C880: Liquid-state plasticizer made by Asahi Denka Co., Ltd., tradename:“ADK-Cizer C880”

C79: Liquid-state plasticizer made by Asahi Denka Co., Ltd., tradename:“ADK-Cizer C79”

Crosslinking agent: Isophorone diisocyanate

A-515: Antifoamer made by BYK-Chemie Japan KK, tradename: “A-515”

Δhardness: Hardness difference between the sheet initial hardness valueand the sheet hardness value after the heat-resistant test TABLE 6(Experiment 3) No. 3-1 3-2 3-3 3-4 3-5 3-6 3-7 3-8 3-9 3-10 ComponentsComponents of Resin 3-A 62 75 0 0 0 0 62 62 0 0 of resin liquid-stateResin 3-B 0 0 62 75 0 0 0 0 0 0 composition resin Resin 3-C 0 0 0 0 6275 0 0 0 0 C880 38 25 38 25 0 0 38 38 0 0 C79 0 0 0 0 38 25 0 0 0 0Toluene solution 0 0 0 0 0 0 0 0 100 0 of the resin Thermo-softening 0 00 0 0 0 0 0 0 100 resin Crosslinking agent 0.86 1.03 0.43 0.52 0.86 1.030.86 0.86 0.69 1.30 A-515 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0 0 Aluminumoxide 200 200 200 200 200 200 0 0 80 200 Boron nitride 0 0 0 0 0 0 100 00 0 Aluminum nitride 0 0 0 0 0 0 0 200 0 0 Gel hardness (F type) 35 5818 28 34 58 35 58 95 90 Sheet moldability ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ x Sheetinitial hardness (C type) 28 38 18 25 29 39 18 35 70 60 Sheet initialthermal conductivity (W/m · K) 1.0 1.1 1.1 1.1 1.1 1.1 1.6 1.9 1.1 1.0Heat Mass loss rate (%) 0.3 0.4 0.4 0.4 0.3 0.3 0.3 0.4 0.6 6.1resistance Sheet hardness 29 39 18 25 30 41 19 37 89 >100 (C type)Thermal conductivity 1.0 1.1 1.1 1.1 1.0 1.1 1.6 1.9 1.1 0.9 (W/m · K)Durability (Δ hardness) 1 1 0 0 1 2 1 2 19 —

Experiment 4 (Experiments Relating to a Resin Composition in whichPolymer (I) is a Crosslinking Polymer (I-b))

No. 4-1

Into a container equipped with a thermometer, a stirring device, a gasintroducing pipe, a reflux condenser and a dropping funnel were charged39.7 parts of 2EHA, 0.3 part of HEA (with a hydroxyl-group-containingmonomer being set to 1-mol % in the entire polymerizable monomers), 50parts of phthalic acid ester-based liquid-state plasticizer (theaforementioned “Vinycizer 124”), and the inner gas of the container wasreplaced with a nitrogen gas. This was heated to 80° C., and a mixtureof 0.05 part of azoisobutyronitrile serving as a polymerizationinitiator and 10 parts of the phthalic acid ester-based liquid-stateplasticizer (the aforementioned “Vinycizer 124”) was charged into thedropping funnel, and dropped into the container in two hours. To thiswas further added 0.02 part of azoisobutyronitrile, and the resultingmixture was heated to 90° C. and allowed to undergo a polymerizationreaction for 3 hours. Prior to the completion of the polymerizationreaction, 60 parts of the liquid-state plasticizer was added thereto andair was further blown thereto to cool the system so that thepolymerization was completed. A mixture of an acrylic polymer containing1 mol % hydroxyl group and a phthalic acid ester-based liquid-stateplasticizer (hereinafter, referred to as acrylic resin No. 4-1) wasobtained. The residual 2EHA, confirmed by gas chromatography (GC), was0.1%, and the acrylic polymer containing 1-mol % hydroxyl group in theacrylic resin No. 4-1 was 24.8%.

The viscosity of the resulting acrylic resin No. 4-1 at 25° C. was 1980mPa·s. With respect to the molecular weight of the polymer measured byGPC, the weight-average molecular weight Mw was 506000 and thenumber-average molecular weight Mn was 201000. Moreover, the glasstransition point temperature of the acrylic polymer containing 1-mol %hydroxyl-group, measured by a differential scanning calorimeteraccording to a conventional method, was −64° C.

Next, 100 parts of acrylic resin No. 4-1, 0.26 part of isophoronediisocyanate serving as a crosslinking agent (in which the amount ofisocyanate was mole equivalent to the amount of hydroxyl groups inacrylic resin No. 4-1) serving as a crosslinking agent, 0.1 part ofdibutyltin laurate serving as a crosslinking accelerator and 1300 partsof aluminum oxide having a thermal conductivity of 30 W/m·K (theaforementioned AS-40) were uniformly kneaded by a pressurized kneader at25° C. for 30 minutes. Thereafter, the kneaded matter was extruded intoa gap between two sheets of PET films by using an extruder to be set toa thickness of 1 mm to obtain a sheet-shaped resin composition for athermal conductive material. Next, the resulting sheet-shaped resincomposition for a thermal conductive material was left at roomtemperature for 24 hours so that the reaction between the hydroxyl groupand the isocyanate group in the composition was completed. The sheet fora thermal conductive material (thermal conductive sheet) thus obtainedwas free from stickiness, and formed a gel-state resin in which theapplied phthalic acid ester-based liquid-state plasticizer was held inthe crosslinking polymer. Moreover, the sheet was uniform without aseparation from the applied thermal conductive filler, and free frombubbles to provide a sheet with superior surface smoothness. In otherwords, the sheet was superior in its moldability.

Next, the thermal conductivity of the resulting sheet was measured by aquick thermal conductivity meter, made by Kyoto ElectronicsManufacturing Co., Ltd, Item No. QTM-500. The thermal conductivity ofthe resulting sheet was 3.2 W/m·K, which was a high level of thermalconductivity.

Next, in order to evaluate the flexibility of the resulting sheet, adurometer hardness test (type-A test) was carried out at 25° C. incompliance with JIS K 6253 by using an Asker rubber A-type hardnesstester made by Koubunshi Keiki Co., Ltd. The pressing stylus of thehardness tester was pushed into the center of the sample so that thepressing face was made in close-contact with the sample; thus, themaximum indicated value within a second from the time of theclose-contact was used as the hardness. Here, the sheet that had beenlaminated to a thickness of 10 mm was used as the sample. The smallerthe hardness value, the more flexible the sheet becomes. The rubberhardness of the sheet obtained in this Example was 60.

Next, in order to measure long-term flexibility of the resulting sheet,the sheet was maintained in an oven at 150° C. for 3 hours. In thiscase, the mass loss rate was 0.7%. Thus, the resulting sheet was alsosuperior in the long-term flexibility.

No. 4-2

The same processes as those of No. 4-1 were carried out except that thealuminum oxide of No. 4-1 was changed to 250 parts of boron nitridehaving a thermal conductivity of 50 W/m·K (made by KCM Corporation; ItemNo. BN-100) so that a sheet for a thermal conductive material wasobtained, and this was subjected to various evaluations. The resultingsheet was free from stickiness, and formed a gel-state resin in whichthe applied phthalic acid ester-based liquid-state plasticizer was heldin the crosslinking polymer. Moreover, the sheet was uniform without aseparation from the applied thermal conductive filler, and free frombubbles to provide a sheet with superior surface smoothness. In otherwords, the sheet was superior in its moldability. The thermalconductivity of this sheet was 3.5 W/m·K, which was a high level ofthermal conductivity. The rubber hardness of the sheet, measured byusing an Asker rubber A-type hardness tester in the same manner as inNo.4-1, was 20. As a result of evaluation on the long-term flexibilityof the resulting sheet, the mass loss rate was 0.8%, and the sheet wassuperior in its long-term flexibility. No. 4-3 The same processes asthose of No. 4-1 were carried out except that the aluminum oxide of No.4-1 was changed to 700 parts of aluminum nitride having a thermalconductivity of 120 W/m·K (made by Toyo Aluminum K.K.; Item No. R-15) sothat a sheet for a thermal conductive material was obtained, and thiswas subjected to various evaluations. The resulting sheet was free fromstickiness, and formed a gel-state resin in which the applied phthalicacid ester-based liquid-state plasticizer was held in the crosslinkingpolymer. Moreover, the sheet was uniform without a separation from theapplied thermal conductive filler, and free from bubbles to provide asheet with superior surface smoothness. In other words, the sheet wassuperior in its moldability. The thermal conductivity of this sheet was3.9 W/m·K, which was a high level of thermal conductivity. The rubberhardness of the sheet, measured by using an Asker rubber A-type hardnesstester, was 45. As a result of evaluation on the long-term flexibilityof the resulting sheet, the mass loss rate was 0.6%, and the sheet wassuperior in its long-term flexibility.

No. 4-4

LMA (39 parts), 1 part of polyethylene glycol dimethacrylate (theaforementioned “Light Ester 9EG”) serving as a polyfunctional monomer, 2parts of t-amyl peroxy 3,5,5-trimethyl hexanate (the aforementioned“Kaya Ester AN”) serving as a polymerization initiator, 60 parts ofphthalic acid ester-based plasticizer (the aforementioned “Vinycizer124”) and 1300 parts of aluminum oxide (the aforementioned AS-40) werekneaded at normal temperature for 30 minutes by using a pressurizedkneader. Next, in the same manner as in No. 4-1, this was extruded intoa gap between 2 sheets of PET films to be set to a thickness of 1 mm byusing an extruder so that a sheet-shaped resin composition for a thermalconductive material was obtained. Next, the resulting sheet was heatedin a furnace at 120° C. for 30 minutes so that the polymerizationcrosslinking reaction was completed. This sheet for a thermal conductivematerial was evaluated in the same manner as in No. 4-1. The resultingsheet was uniform without a separation from the applied thermalconductive filler, and free from stickiness and bubbles to provide asheet with superior surface smoothness. In other words, the sheet wassuperior in its moldability. The thermal conductivity of this sheet was3.1 W/m·K, which was a high level of thermal conductivity. The rubberhardness of the sheet, measured by using an Asker rubber A-type hardnesstester, was 62. As a result of evaluation on the long-term flexibilityof the resulting sheet, the mass loss rate was 0.8%, and the sheet wassuperior in its long-term flexibility.

No. 5 (for Use in Comparison)

Into a container equipped with a thermometer, a stirring device, a gasintroducing pipe, a reflux condenser and a dropping funnel were charged39.7 parts of 2EHA, 0.3 part of HEA (with a hydroxyl-group-containingmonomer being set to 1 mol % in the entire monomers), 50 parts oftoluene and 0.3 part of a-methyl styrene serving as a chain transferagent, and the inner gas of the container was replaced with a nitrogengas. This was heated to 80° C., and a mixture of 0.05 part ofazoisobutyronitrile serving as a polymerization initiator and 10 partsof toluene was charged into the dropping funnel, and dropped into thecontainer in two hours. To this was further added 0.01 part ofazoisobutyronitrile, and the resulting mixture was heated to 90° C. andallowed to undergo a polymerization reaction for 3 hours. Prior to thecompletion of the polymerization reaction, air was blown thereto to coolthe system so that the polymerization was completed. Next, the toluenewas completely distilled off under reduced pressure of the system toobtain a polymer that was in a solid state with 1-mole % hydroxyl groupscontained therein. Here, Mw of the polymer, determined by GPC, was106000, and Mn thereof was 51000. Moreover, the glass transition pointtemperature of the polymer, measured by a differential scanningcalorimeter according to a conventional method, was −60° C.

Next, 100 parts of the resulting polymer, 0.65 part of isophoronediisocyanate (in which the amount of isocyanate was mole equivalent tothe amount of hydroxyl groups) serving as a crosslinking agent, 0.3 partof dibutyltin laurate serving as a crosslinking accelerator, 25 parts ofparaffin (the aforementioned paraffin wax 115) that served as athermosoftening agent with a melting point of 47° C. and 1300 parts ofaluminum oxide having a thermal conductivity of 30 W/m·K (theaforementioned AS-40) were kneaded by a pressurized kneader at 50° C.for 30 minutes. Thereafter, the kneaded matter was extruded into a gapbetween two sheets of PET films by using an extruder to be set to athickness of 1 mm to obtain a sheet-shaped resin composition for athermal conductive material. Next, the resulting sheet-shaped resincomposition for a thermal conductive material was left at roomtemperature for 24 hours so that the reaction between the hydroxyl groupand the isocyanate group in the composition was completed. The sheetthus obtained was evaluated in the same manner as in No. 4-1.

Although the resulting sheet was uniform without a separation betweenthe resin and the applied thermal conductive filler, there wereirregularities and bubbles on the surface to cause degradation in thesurface smoothness. In other words, the sheet was poor in itsmoldability. The thermal conductivity of this sheet was 3.1 W/m·K, whichwas a high level of thermal conductivity. When the rubber hardness ofthe sheet was measured by using an Asker rubber A-type hardness testerat 25° C., the measured value exceeded 100, which was the limit ofmeasurements, making the measurement unoperable; therefore, the rubberhardness was measured at 50° C. The rubber hardness of this sheet at 50°C. was 65. Consequently, it was found that the resulting sheet was poorin its flexibility. As a result of evaluation on the long-termflexibility of the resulting sheet, the mass loss rate was 0.9%, and thesheet was superior in its long-term flexibility; however, a number ofswellings occurred on the sheet after the measurement.

No. 4-6

Into a container equipped with a thermometer, a stirring device, a gasintroducing pipe, a reflux condenser and a dropping funnel were charged38.81 parts of 2EHA, 1.04 parts of HEA (with a hydroxyl-group-containingmonomer being set to 4 mol % in the entire monomers), 50 parts of atrimellitic acid ester-based liquid-state plasticizer (theaforementioned “ADK-Cizer C880”) serving as a liquid-state plasticizerand 0.15 part of α-methyl styrene dimer serving as a chain transferagent, and the inner gas of the container was replaced with a nitrogengas.

This was heated to 75° C., and a mixture of 0.1 part ofdimethyl-2,2′-azobis(2-methylpropionate) serving as a polymerizationinitiator and 10 parts of the liquid-state plasticizer (theabove-mentioned “ADK-Cizer C880”) was charged into the dropping funnel,and dropped in 1.5 hours. To this was further added 0.03 part ofdimethyl-2,2′-azobis(2-methylpropionate) serving as a polymerizationinitiator, and the resulting mixture was heated to 90° C. and allowed toundergo a polymerization reaction for 2 hours.

Prior to the completion of the polymerization reaction, 60 parts of theliquid-state plasticizer (the above-mentioned “ADK-Cizer C880”) wasadded thereto, and air was blown thereto to cool the system so that thepolymerization was completed; thus, a mixture of a 4-mol %hydroxyl-group-containing acrylic polymer and the liquid-stateplasticizer (hereinafter, referred to as acrylic resin No. 4-2) wasobtained. The residual 2EHA, confirmed by gas chromatography (GC), was0.1%, and the polymer containing 4-mol % hydroxyl group in acrylic resinNo. 4-2 was 24.8%. The viscosity of the resulting acrylic resin No. 2 at25° C. was 2400 mPa·s. Mw of the polymer, determined by GPC, was 375000and the number-average molecular weight Mn was 93000. Moreover, theglass transition point temperature, measured by a differential scanningcalorimeter according to a conventional method, was −58° C.

The above-mentioned acrylic resin No. 4-2 (100 parts), 0.06 part ofdibutyltin dilaurate serving as a crosslinking accelerator, 0.1 part ofan antifoamer (the aforementioned “A-515”), 0.57 part of hexamethylenediisocyanate (in which the amount of isocyanate was mole equivalent tothe amount of hydroxyl groups of the polymer) serving as a crosslinkingagent and 600 parts of aluminum oxide having a thermal conductivity of30 W/m·K (the aforementioned AS-40) were uniformly kneaded at a rotationspeed of 300 rpm for 5 minutes using a Three-one Motor (Item No. 600 G)made by Shinto Scientific Co., Ltd.

Next, the resulting resin composition was placed still in a reducedpressure desiccator the degree of vacuum of which was set to 0.09 MPafor 10 minutes so as to be defoamed, and applied onto a PET film thathad been subjected to a releasing treatment by using a bar coater thatwas set to prepare a thickness of 1 mm. This coated product was heatedat 100° C. for two hours to allow the polymer containing hydroxyl groupsand hexamethylene diisocyanate to react with each other in thecomposition so that a sheet for a thermal conductive material wasobtained. The resulting sheet was free from stickiness, and formed agel-state resin in which the liquid-state plasticizer was held in thecrosslinking polymer. Moreover, the sheet was uniform without aseparation from the applied thermal conductive filler, and free frombubbles to provide a sheet with superior surface smoothness. In otherwords, the sheet was superior in its moldability. The thermalconductivity of the sheet was 1.8 W/m·K, which was a high level ofthermal conductivity.

Moreover, with respect to the evaluation on the heat resistance of thesheet that had been exposed to a high temperature of 130 ° C. for a longperiod of time (100, 500 or 1000 hours), the change in hardness and themass loss rate (the same as described earlier) were measured, and theresults are shown in Table 7. With respect to the hardness, sheets, eachhaving a thickness of 1 mm, were laminated to a thickness of 10 mm toprepare a measuring sample, and this sample was measured by using anAsker rubber C-type hardness tester made by Koubunshi Keiki Co., Ltd. at25° C. in compliance with a hardness test type-C indicated by JIS K 7312(7). The pressing stylus of the hardness tester was pushed into thecenter of the sample so that the pressing face was made in close-contactwith the sample; thus, the maximum indicated value within a second fromthe time of the close-contact was used as the hardness.

Based upon the initial hardness and the respective measured results onthe hardness obtained after the sheet had been left in an oven heated to130° C. for 100 hours, 500 hours and 1000 hours respectively, the changein hardness was calculated, and the value of the initial hardness andthe change in hardness are shown in Table 7. The minus value in thechange in hardness indicates that the sample becomes soft. As the changein hardness and the mass loss rate become smaller, the sheet heatresistance becomes better, making it possible to exert a stableheat-releasing property for a long period of time. Here, this evaluationon the heat resistance was carried out on each of the above-mentionedNos. 4-1 to 4-4 and No. 4-5 for use in comparison, and the results arealso shown in Table 7.

No. 4-7

The same processes as those of No. 4-6 were carried out except that inNo. 4-6, 0.06 part of dibutyltin dilaurate serving as a crosslinkingaccelerator was changed to 0.01 part and that 0.1 part ofN,N,N′,N′-tetramethyl-1,6-hexane diamine (made by Tosoh Corporation;“TOYOCAT-MR”) was used as a compound having an atom with a lone pair inits molecule so that a sheet for a thermal conductive material wasobtained. The sheet moldability was superior as it was in No. 4-6, andthe thermal conductivity was 1.8 W/m·K. The results of evaluations areshown in Table 7.

No. 4-8

The same processes as those of No. 4-7 were carried out except that inNo. 4-7, the compound having an atom with a lone pair in its moleculewas changed to 0.5 part of N,N,N′-trimethylaminoethylmethanol amine(made by Tosoh Corporation; “TEDA-RX5”) so that a sheet for a thermalconductive material was obtained. The sheet moldability was superior asit was in No.4-7, and the thermal conductivity was 1.9 W/m·K. Theresults of evaluations are shown in Table 7.

No. 4-9

The same processes as those of No. 4-7 were carried out except that inNo. 4-7, the compound having an atom with a lone pair in its moleculewas changed to 0.5 part of hexamethyl phosphor amide so that a sheet fora thermal conductive material was obtained. The sheet moldability wassuperior as it was in No. 4-7, and the thermal conductivity was 1.7W/m·K. The results of evaluations are shown in Table 7.

No. 4-10

The same processes as those of No. 4-7 were carried out except that inNo. 4-7, the compound having an atom with a lone pair in its moleculewas changed to 0.5 part of acetyl acetone so that a sheet for a thermalconductive material was obtained. The sheet moldability was superior asit was in No.4-7, and the thermal conductivity was 1.7 W/m·K. Theresults of evaluations are shown in Table 7. TABLE 7 (Experiment 4)Hardness Hardness change; 130° C. Mass loss rate (%); 130° C. measuringInitial 100 hours 500 hours 1000 hours 100 hours 500 hours 1000 hoursNo. conditions hardness later later later later later later 4-1 A-type:25° C. 60 −2 −7 −15 0.7 1.2 2.5 4-2 A-type: 25° C. 20 0 −2 −9 0.9 2.13.5 4-3 A-type: 25° C. 45 −1 −5 −13 0.8 1.5 2.9 4-4 A-type: 25° C. 62 −2+3 +15 0.7 1.2 2.6 4-5 A-type: 25° C. 65 0 +13 +28 1.9 2.9 4.6 4-6C-type: 25° C. 45 0 −2 −18 0.55 0.64 0.78 4-7 C-type: 25° C. 46 0 +1 −30.54 0.63 0.72 4-8 C-type: 25° C. 45 +1 −2 −6 0.50 0.66 0.77 4-9 C-type:25° C. 47 −2 +1 −3 0.53 0.62 0.78 4-10 C-type: 25° C. 48 0 −2 −5 0.560.69 0.80

As clearly indicated by Table 7, Examples of the present invention makeit possible to provide a resin composition for thermal conductivematerial that is superior in thermal conductivity, flexibility andmoldability efficiently. In contrast, Nos. 4 and 5 for use incomparison, which use a thermal softening agent without using an oilysubstance that is in a liquid state at normal temperature, are inferiorin comparison with Examples of the present invention. Moreover, by usinga compound having an atom with a lone pair in its molecule, it becomespossible to suppress the gel-state resin from deteriorating in hardness.

Experiment 5 (Experiments Relating to a Resin Composition in whichPolymer (I) is a Crosslinking Polymer (I-b)) Synthesis Example 6

Into a container equipped with a thermometer, a stirring device, a gasintroducing pipe, a reflux condenser and a dropping funnel were charged39.22 parts of 2EHA, 0.78 part of 2-hydroxyethyl acrylate (with ahydroxyl-group-containing monomer being set to 3 mol % in the entirepolymerizable monomers), 50 parts of trimellitic acid ester-basedliquid-state plasticizer (the aforementioned “ADK-Cizer C880”) and 0.15part of a-methylstyrene dimer serving as a chain transfer agent, and theinner gas of the container was replaced with a nitrogen gas. This washeated to 75° C., and a mixture of 0.1 part of dimethyl2,2′-azobis(2-methyl propionate) serving as a polymerization initiatorand 10 parts of trimellitic acid-based ester liquid-state plasticizer(the aforementioned “ADK-Cizer C880”) was charged into the droppingfunnel, and dropped into the container in 1.5 hours. To this was furtheradded 0.03 part of dimethyl-2,2′-azobis(2-methylpropionate), and theresulting mixture was heated to 90° C. and allowed to undergo apolymerization reaction for 2 hours.

Prior to the completion of the polymerization reaction, 0.05 part ofdibutyltin dilaurate was added thereto as an organic metal compound, andair was blown thereto to cool the system so that the polymerization wascompleted; thus, a (meth)acrylic resin (hereinafter, referred to asresin 5-A) was obtained. The residual 2EHA, confirmed by gaschromatography (GC), was 0.1%, and the polymer containing 3-mol %hydroxyl group in the resin 5-A, was 39.9%. The viscosity of theresulting resin 5-A at 25° C. was 6100 mPa·s. With respect to themolecular weight of the polymer measured by GPC, the weight-averagemolecular weight Mw was 356000 and the number-average molecular weightMn was 91000. Moreover, the glass transition point temperature of thepolymer, measured by a differential scanning calorimeter according to aconventional method, was −60° C.

No. 5-1

The above-mentioned resin No. 5-A (100 parts), 0.1 part of an antifoamer(the aforementioned “A-515”), 0.57 part of hexamethylene diisocyanate(in which the amount of isocyanate was 1.0 equivalent to the amount ofhydroxyl groups in the polymer), 0.25 part of acetic acid (boilingpoint: 119° C.) serving as an acidic compound and 200 parts of aluminumoxide having a thermal conductivity of 30 W/m·K (made by Showa DenkoK.K.; Item No. AS-10) were uniformly kneaded at a rotation speed of 300rpm for 5 minutes using a Three-one Motor (Item No. 600 G) made byShinto Scientific Co., Ltd. The viscosity, pot life at 25° C. anddefoaming property of the resulting resin composition were measuredunder conditions as described below, and the results are shown in Table8.

[Viscosity]

The viscosity of the resulting resin composition at 25° C. was measuredby using a B-type viscometer under conditions of rotor No. 4 and numberof revolutions of 6 rpm. When the viscosity is set to a low level, theresulting resin composition not only achieves a superior operability,but also allows a thermal conductive filler to be filled in a highproportion; thus, it becomes possible to improve the heat-radiatingproperty (thermal conduction), and also to achieve an easy defoamingperformance, which easily removes air contained in the resin compositionupon manufacturing.

[Pot Life at 25° C.]

The resulting resin composition was stored in a water vessel that wastemperature-adjusted to 25° C., and subjected to a viscosity measurementwith elapsed time under the same condition as the above viscositymeasurement so that the time at which a viscosity increase of 20% ormore from the initial viscosity value has been confirmed was defined asthe pot life (applicable time). Here, in the case when the viscosityincrease after an elapsed time of 8 hours was less than 10%, this casewas evaluated as 8 hours or longer. For example, when the applicabletime is longer, a large amount of production was available at one lot,making it possible to provide a superior resin composition in economicalefficiency.

[Defoaming Property]

The resulting resin composition was placed still in a reduced-pressuredesiccator set to 0.09 MPa in its degree of vacuum, and defoamingprocesses were respectively carried out for 2 minutes, 5 minutes and 10minutes so that the presence of bubbles contained in each of the resincompositions was visually observed. When no bubbles were visuallyobserved, this case was defined as ◯, and when even slight bubbles wereobserved, this case was defined as X. For example, when no bubbles areobserved even after a short period of defoaming process, it becomespossible to provide a superior resin composition in productivity.

Next, the resulting resin composition was subjected to a defoamingprocess for 2 minutes as well as for 10 minutes under the followingdefoaming conditions, and each of these was then applied to a PET filmthat had been subjected to a releasing treatment, by using a bar coaterdesigned to prepare a thickness of 1 mm. Next, each of these coatedproducts was heated at 100° C. for two hours so that the polymer havinga hydroxyl group in the composition was allowed to react withhexamethylene diisocyanate to provide a sheet-shaped cured product ofthe resin composition. The moldability of the sheet thus obtained wasevaluated in the same manner as in the aforementioned Experiment 1. Theresults are shown in Table 8. Moreover, with respect to the sheetobtained through the defoaming time of 10 minutes, the initial thermalconductivity, sheet initial hardness, heat resistance and durabilitywere evaluated in the same manner as in the aforementioned Experiment 1.Here, the evaluation on heat resistance was conducted at 100° C. for 168hours. The results are shown in Table 8.

No. 5-2

The same processes as those of No. 5-1 were carried out except that theacidic compound was changed from acetic acid to propionic acid (boilingpoint 141° C.) (0.25 part) so that a resin composition and asheet-shaped cured product of the resin composition were obtained. Thesewere evaluated in the same manner as in No. 5-1, and the results areshown in Table 8.

No. 5-3

The same processes as those of No. 5-1 were carried out except that theamount of the thermal conductive filler was changed from 200 parts to300 parts so that a resin composition and a sheet-shaped cured productof the resin composition were obtained. These were evaluated in the samemanner as in No. 5-1, and the results are shown in Table 8.

No. 5-4 (for use in Comparison)

The same process as those of No. 5-1 were carried out except that noacidic compound was used so that a resin composition and a sheet-shapedproduct of the resin composition were obtained. These were evaluated inthe same manner as in No. 5-1, and the results are shown in Table 8.When compared with any one of the examples of the present invention, theresulting resin composition had higher viscosity, was inferior inoperability, took a longer period of time so as to be completelydefoamed, and had a shorter pot life. Consequently, these were inferiorin productivity and caused high costs in comparison with any one ofExamples of the present invention.

Moreover, the cured product made by setting the defoaming time to 2minutes was inferior in moldability. It is considered that this iscaused by bubbles contained in the cured product.

No. 5-5 (for use in Comparison)

The same process as those of No. 5-1 were carried out except that noacidic compound was used and that the amount of the thermal conductivefiller was changed from 200 parts to 300 parts so that a resincomposition and a sheet-shaped product of the resin composition wereobtained. These were evaluated in the same manner as in No. 5-1, and theresults are shown in Table 8. The resulting resin composition hadinsufficient dispersion of the filler and higher viscosity in comparisonwith any of Examples of the present invention (exceeding the uppermeasuring limit of the device to become unmeasurable), and even when thedefoaming time was set to 10 minutes, the presence of bubbles wasobserved. Moreover, it was confirmed that the pot life was shorter incomparison with any one of Examples of the present invention.Consequently, these were inferior in productivity and caused high costs.Furthermore, it was confirmed that the resulting cured product wasinferior in moldability and had a poor thermal conductive performance.It is considered that this was caused by bubbles contained in the curedproduct.

Here, the meanings of abbreviations used in Table 8 are explained asfollows:

HDI: Hexamethylene diisocyanate

A-515: Antifoamer made by BYK-Chemie Japan KK, tradename: “A-515”

Δhardness: Hardness difference between a sheet initial hardness valueand the sheet hardness value after the heat-resistant test TABLE 8(Experiment 5) No. 5-1 5-2 5-3 5-4 5-5 Resin 5-A 100 100 100 100 100 HDI0.57 0.57 0.57 0.57 0.57 A-515 0.1 0.1 0.1 0.1 0.1 Acetic acid 0.25 00.25 0 0 Propionic acid 0 0.25 0 0 0 Alumina oxide 200 200 200 200 200Viscosity (Pa · s) 20.5 21.5 46.9 50.2 Unmeas- urable Defoaming property 2 minutes ∘ ∘ ∘ x x  5 minutes ∘ ∘ ∘ x x 10 minutes ∘ ∘ ∘ ∘ x Pot life(25° C.) 8 hours 8 hours 8 hours 1 hr 0.5 hr or more or more or moreSheet moldability  2 minutes ∘ ∘ ∘ x1 x2 10 minutes ∘ ∘ ∘ ∘ x2 Sheetinitial 12 11 23 12 30 hardness (C-type) Sheet initial 0.85 0.81 1.200.85 0.95 thermal conductivity (W/m · K) Heat resistance Mass loss rate(%) 0.15 0.12 0.11 0.12 0.13 Sheet hardness 12 12 25 13 33 (C-type)Thermal 0.88 0.82 1.23 0.82 0.91 conductivity (W/m · K) Durability (Δ 01 2 1 3 hardness)x1: Irregularities and bubbles were observed on the sheet surface.x2: Separated liquid-state plasticizer appeared on the surface, orseparation andprecipitation of the filler were observed.

As clearly indicated by Table 8, Examples of the present invention makeit possible to efficiently provide a cured product (thermal conductivematerial) for thermal conductive material that is superior inoperability and productivity upon producing a composition for a thermalconductive material, and achieves superior moldability, flexibility,thermal conductivity and decay durability. In comparison with Examplesof the present invention, any of Comparative Examples are inferior inoperability and productivity upon producing a composition for a thermalconductive material, and the resulting cured products are also inferiorin moldability and thermal conductivity.

INDUSTRIAL APPLICABILITY

By using the resin composition of the present invention, it becomespossible to obtain a thermal conductive material that is superior inthermal conductivity and flexibility. Therefore, this material iseffectively used as a thermal conductive material that is interposedbetween a heat-generating body, such as an electric and an electronicpart and a heat-radiating body, such as a heat sink, a radiating fin anda metal heat radiating plate, so that heat generated in the electric andelectronic parts is radiated. Moreover, this material is also applied asvarious other heat conductive materials.

1. A resin composition for a thermal conductive material, comprising: apolymer (I), a liquid-state plasticizer (II) and a thermal conductivefiller (III) having a thermal conductivity of 20 W/m·K or more, whereinthe liquid-state plasticizer (II) is in a liquid state at 25° C., andhas a mass loss rate of 2 mass % or less, when kept at 130° C. for 24hours.
 2. The resin composition for a thermal conductive materialaccording to claim 1, wherein a viscosity of the liquid-stateplasticizer (II) at 25° C. is set to 1000 mPa·s or less.
 3. The resincomposition for a thermal conductive material according to claim 1,wherein the polymer (I) is a (meth)acrylic polymer (I-a), and furthercomprises a polymerizable monomer (IV).
 4. The resin composition for athermal conductive material according to claim 3, wherein the(meth)acrylic polymer (I-a) is obtained by radical polymerization in theliquid-state plasticizer (II).
 5. The resin composition for a thermalconductive material according to claim 3, wherein the (meth)acrylicpolymer (I-a) has a glass transition point of 0° C. or less, and atleast one portion of the polymerizable monomer (IV) is composed of a(meth)acrylic acid alkyl ester wherein an alkyl group has 2 to 18 carbonatoms.
 6. The resin composition for a thermal conductive materialaccording to claim 3, further comprising a radical polymerizationinitiator (V).
 7. The resin composition for a thermal conductivematerial according to claim 1, wherein the polymer (I) is a crosslinkingpolymer (I-b), and which comprises a crosslinking agent (VI) capable ofreacting with the crosslinking polymer (I-b).
 8. The resin compositionfor a thermal conductive material according to claim 7, wherein thecrosslinking polymer (I-b) is obtained by copolymerizing a polymerizablemonomer (I-b-1) with a polymerizable monomer (I-b-2) having a functionalgroup for crosslinking, and the polymerizable monomer (I-b-2) iscontained in a range from 0.01 to 5 mole % based on 100 mole % of thetotal amount of the polymerizable monomer (I-b-1) and the polymerizablemonomer (I-b-2).
 9. The resin composition for a thermal conductivematerial according to claim 8, wherein the functional group of thepolymerizable monomer (I-b-2) is a hydroxyl group, the crosslinkingagent (VI) is a compound containing an isocyanate group, and whichfurther comprises an organic compound and a compound having an atom witha lone pair in the molecule thereof as a catalyst used for the reactionbetween the crosslinking agent (VI) and the crosslinking polymer (I-b).10. The resin composition for a thermal conductive material according toclaim 7, further comprising an acidic compound.
 11. A thermal conductivematerial, which is formed by curing the resin composition for a thermalconductive material according to claim
 1. 12. The thermal conductivematerial according to claim 11, which has a mass loss rate of 5% by massor less when held at 130° C. for 168 hours.
 13. A material for the resincomposition for a thermal conductive material according to claim 4,comprising: the liquid-state plasticizer, the (meth)acrylic polymer(I-a) and the polymerizable monomer (IV).
 14. A material for the resincomposition for a thermal conductive material according to claim 7,comprising: the liquid-state plasticizer (II) and the crosslinkingpolymer (I-b).
 15. The resin composition for a thermal conductivematerial according to claim 2, wherein the polymer (I) is a(meth)acrylic polymer (I-a), and further comprises a polymerizablemonomer (IV).
 16. The resin composition for a thermal conductivematerial according to claim 4, wherein the (meth)acrylic polymer (I-a)has a glass transition point of 0° C. or less, and at least one portionof the polymerizable monomer (IV) is composed of a (meth)acrylic acidalkyl ester wherein an alkyl group has 2 to 18 carbon atoms.
 17. Theresin composition for a thermal conductive material according to claim4, further comprising a radical polymerization initiator (V).
 18. Theresin composition for a thermal conductive material according to claim5, further comprising a radical polymerization initiator (V).
 19. Theresin composition for a thermal conductive material according to claim2, wherein the polymer (I) is a crosslinking polymer (I-b), and whichcomprises a crosslinking agent (VI) capable of reacting with thecrosslinking polymer (I-b).
 20. The resin composition for a thermalconductive material according to claim 8, further comprising an acidiccompound.
 21. The resin composition for a thermal conductive materialaccording to claim 9, further comprising an acidic compound.